McEnroe upbeat on future of tennis despite Federer exit

John McEnroe says Roger Federer and Serena Williams are "irreplaceable" but that tennis "goes on no matter what" as the Swiss prepares to play his final match on Friday.

Federer, a 20-time Grand Slam singles champion, will bring the curtain down on his glittering career in the Laver Cup at London's O2 arena alongside long-time rival Rafael Nadal.

The two players, representing Team Europe, will take on Team World's Frances Tiafoe and Jack Sock in doubles in the evening session on the first day of the event.

The 41-year-old Federer's retirement comes hot on the heels of a similar decision by Williams, who won 23 majors in singles.

McEnroe, who is captain of Team World, admitted the sport would miss the two players but is optimistic about the future, just weeks after 19-year-old Spaniard Carlos Alcaraz won the US Open.

"These two players are irreplaceable," he said. "I don't think there is any question about that."

But he added: "The sport goes on no matter what, and we have witnessed that in every sport over time.

"The opportunity is there to market these young kids in a way that I don't think we have successfully done before."

McEnroe, who won seven Grand Slam singles titles, said Williams had "brought electricity" to the recent US Open, where she lost in the third round.

But he said other players such as Alcaraz and America's Tiafoe, who lost to the Spaniard in the semi-finals at Flushing Meadows, made it an "electrifying event".

Taylor Fritz, who is also part of Team World, said the two big retirements would be tough on a lot of fans but the future was bright.

Federer fans

"Serena and Roger probably have more fans than anybody in tennis," said the American. "But, you know, there's so many more players.

"I think tennis is becoming