At Thursday's draw, it was confirmed that Federer will join Nadal for Team Europe against the American pair of Frances Tiafoe and Jack Sock for Team World on Friday night. Federer, a 20-time Grand Slam champion, will then be replaced by Italy's Matteo Berrettini for the rest of the event.
"It's super special playing with Rafa," Federer said in a news conference. "... To be able to do that one more time, I'm sure it's going to be wonderful."
Said Nadal: "Tomorrow is going to be a special thing. Difficult. Going to be difficult to handle everything, especially for Roger, without a doubt. But for me too. At the end, one of the most important players -- if not the most important player -- in my tennis career is leaving."
Federer, 41, who announced last week that he is retiring because of an ongoing right knee issue, had said Wednesday that playing alongside 22-time Slam champion Nadal would be a unique, fitting way to go out.
"For as long as we battled together, having had always this respect for one another, our families, coaching teams, for us as well to go through a career we both have had, come out the other side and have a nice relationship, is maybe a great message to tennis and beyond," Federer said.
The three-day team event will begin Friday afternoon at The O2 Arena with two singles matches. Norwegian Casper Ruud, the runner-up at the US Open earlier this month, will play Sock in the opener before Stefanos Tsitsipas of Greece takes on Argentina's Diego Schwartzman.
"I'm not sure if I can handle it all, but I'll try," Federer said Thursday about his sure-to-be-emotional on-court farewell.
Tiafoe, a 24-year-old American who beat Nadal en route to his first Grand Slam semifinal at the US Open this month, deadpanned about the matchup, "Yeah, I'm just excited to play two up-and-comers tomorrow," before adding, "It's going to be iconic to be a part of that. Both guys are absolute legends."
Federer and Nadal played each other in singles 40 times (Nadal won 26), including 14 Grand Slam matchups (Nadal won 10, going 6-3 in finals). Nadal came out on top in their classic 2008 Wimbledon final, considered by some the greatest match in history, while Federer won their last showdown, in the 2019 semifinals at the All England Club. They also played one other doubles match together, defeating Jack Sock and Sam Querrey at the inaugural Laver Cup in 2017.
"To be part of this historic moment," Nadal said about Friday, "is going to be something amazing, unforgettable."
The Associated Press contributed to this report.