Welcome Back to the Champions League. Please Maintain Social Distance.

Those final few minutes, just before kickoff, have been mapped out with almost military precision. At exactly 8:50 p.m. local time, a disinfected Champions League match ball will be placed on a ceremonial plinth. At 8:53 p.m., the players will leave their locker rooms. The teams will enter the field, separately, no more than two and a half minutes later.

At 8:57 p.m., as the strains of the Champions League anthem blare out of the stadium’s speakers, the players will face the stands — all but empty — while maintaining social distancing: a meter between each player. Team photos are at 8:57 p.m. and 50 seconds but the photojournalists do not have long to take them: the coin toss is at 8:58.

And then, at 9 p.m. local time on Wednesday, European soccer will enter uncharted territory. After months of planning, weeks of uncertainty, hours of meetings and hundreds upon hundreds of pages of protocols and instructions, the strangest, most intense Champions League in history will finally begin its (belated) push to the final.

Rather than providing a slow-burn climax to the European season, with the final three rounds of games held over almost two months and staged across the continent, the Champions League, the most coveted prize in club soccer, will be settled in only 10 days and in one city: Lisbon.

If, that is, the coronavirus allows it. Already one team is facing a possible outbreak: Atlético Madrid reported Sunday that two members of its traveling party had tested positive.

Per the rules, the two players — Angel Correa and Sime Vrsaljko — were isolated from the rest of the team, and on Monday Atlético announced that it would return to training and continue its preparations for a Thursday quarterfinal against RB Leipzig. That, too, is allowed; even amid a locker-room outbreak, a team can keep playing as long as the club can field 11 starters and two reserves who test negative.

The entire knockout round, in fact, is an abrupt break from history, and not one UEFA — the competition’s organizer, and European soccer’s governing body — is eager to repeat. Nor is it quite as pure a Champions League as anyone might have hoped, since there are vast differences in the preparations of the eight teams that have made it. Paris St.-Germain, which plays the opening match against Italy’s Atalanta on Wednesday, has played only two competitive games since March. Bayern Munich had a monthlong break between the German Cup final and its meeting with Chelsea on Saturday, a layoff that Oliver Kahn, the club’s forthcoming chief executive, worries might be a disadvantage.

The teams from England, Italy and Spain, meanwhile, might complain of a lack of rest. The Serie A season only finished on the first weekend of August, after a grueling schedule of 10 games in little more than six weeks. The Premier League campaign ended in the last week of July.

And then, of course, there are the myriad demands being placed on the teams to ensure the tournament can play to a finish. “I have a feeling that whichever team handles all of these fears and responsibilities the best has a big chance to win,” Kahn said.

Those requirements touch almost every aspect of each team’s preparation. Last week, representatives of all 12 clubs still involved in the competition at that stage joined an online call with UEFA, European soccer’s governing body, to go over what the tournament would look like.

They were presented with three sets of slides, amounting to more than 130 pages — as well as being sent the 31-page “Return To Play” protocol governing almost every aspect of their stay in Portugal.

As well as detailing where each team will stay and train in the city, the slides informed them that they would be afforded 210 bottles of water, as well as 90 bottles of Gatorade, every day at their appointed training facility; that they can ask for up to 50 kilograms of ice to be made available during training sessions and games; and that they must supply not only photos but the dimensions of their team buses, if they were planning on providing their own.

They were presented with maps of the stadiums they will use, detailing where, precisely, their players will be allowed to warm up. So-called “fast feet” exercises must take place away from the playing surface, and the area in front of each goal-mouth must not be touched. Players will not be permitted to perform warm downs on the field at all, to protect the turf as much as possible for other matches.

They were walked through the testing schedule for each of their players — one before setting off for Lisbon, one immediately upon arrival, one the day before each game. The results will be returned to them no more than six hours before kickoff — to ensure that the competition does not see an outbreak of the sort that has disrupted several major sports in the United States.

UEFA has a procedure in place should a team record a positive test: Its game will go ahead, with that player (or players) not involved. Games will only be canceled if a team cannot name 13 fit players. In that situation, the team that cannot proceed will forfeit. The result will be recorded as a 3-0 defeat. UEFA, the meeting made clear, has a procedure for almost anything.

There is a good reason for that. The organization has put far too much work in for the competition not to play to a finish, for Europe to be devoid of a champion. It has not only been a monumental effort in terms of planning, but in terms of politics, too.

The day after Atlético Madrid eliminated Liverpool, last year’s winner, in March, the idea that the Champions League might be completed seemed a fanciful one. The coronavirus pandemic had brought soccer to a halt across Europe, and the continent’s showpiece competition was frozen midway through its round of 16.

As the hiatus dragged on and leagues tried to pick a way back to action, the Champions League appeared, if anything, in even greater peril. UEFA had publicly stated its commitment to playing out the competition — the financial consequences of failure to do so were too much to contemplate — but the path ahead was anything but clear.

By May, UEFA had realized there was only one available conclusion. The tournament had to be wrapped up in a maximum of three weeks. Unlike the domestic competitions that were returning, it had to corral teams from multiple countries, with differing regulations on containing the virus. It would have to be a knockout competition, a series of one-and-done games played in a single country, more akin to the closing stages of a World Cup.

Turkey was convinced it could host such a tournament: the Champions League final had, after all, been scheduled for Istanbul before the pandemic struck. UEFA, though, was skeptical. Turkey was regarded as too much of a risk. Germany, Spain, Hungary and Portugal all volunteered to take its place, and Turkey agreed to step aside, promised next year’s final instead.

At the same time, Portuguese officials made their move. Fernando Gomes and Tiago Craveiro, the president and chief executive of the country’s soccer federation, had developed a close relationship with UEFA’s leadership. They stressed to them that Portugal, at that point, had not been as hard hit as other nations, and that Lisbon had experience hosting major events. The pitch worked.

With a format and a venue, UEFA now had to take care of the organization. In ordinary circumstances, that might take months. It had only a few weeks. A hosting agreement, including tax breaks, was hammered out with the Portuguese government and a detailed health protocol was created. The games, UEFA announced, would take place without fans.

To avoid complaints of favoritism and petty arguments among the teams, hotels were allocated slots in the competition draw, meaning where each team would stay and train would be as much a case of luck of the draw as the opponents it would face.

Then there was the matter of assuaging UEFA’s broadcast partners. Some had already secured clawbacks and rebates from the national leagues, but UEFA managed to strike a deal. Millions of dollars will have to be returned, but just how much will depend on the success of this month’s tournament. The final figure will determine the total prize money teams will receive.

In July, though, all the work suddenly appeared to be under threat. Portugal had an alarming spike in coronavirus cases, centered on Lisbon. The country’s authorities imposed a curfew in the city, and some began asking if Portugal should host the event at all.

UEFA’s leadership, led by its president, Aleksander Ceferin, held a call with senior Portuguese officials, including the prime minister, Antonio Costa. The soccer officials provided a detailed presentation, involving mountains of statistics and graphics, that, they said, showed Portugal’s testing record and handling of the virus meant there was little threat to the tournament.

That final hurdle cleared, UEFA could press on. On Aug. 4, it presented the final version of what its emergency Champions League would look like to the clubs. The focus was on all of the sudden norms of this new world: face masks and hand sanitizing and social distancing.

There will be just one nod to the past. At 8:50 p.m., precisely 10 minutes before kickoff of each match, a match ball will be placed on its plinth. On the ball’s curved surface, just beneath an image of the Champions League trophy, two words will serve as a reminder that this is not how it was supposed to be. “Istanbul 2020,” it will read.