Roger Federer won't play again until 2021 after having another knee procedure

"A few weeks ago, having experienced a setback during my initial rehabilitation, I had to have an additional quick arthroscopic procedure on my right knee," Federer tweeted along with a promise to return in 2021. "Now, much like I did leading up to the 2017 season, I plan to take the necessary time to be 100% ready to play at my highest level."

The 20-time Grand Slam winner spent most of the 2016 season recovering from a knee injury and returned in 2017 to win the Australian Open and Wimbledon. Federer, 38, last played in the Australian Open in January, losing in a semifinal to Novak Djokovic. His next appearance will presumably be in the 2021 Australian Open, which begins Jan. 18 in Melbourne.

Professional tennis was suspended in March and will be shut down until at least the end of July because of the coronavirus pandemic. It upset the schedule of the sport's four major tournaments with Wimbledon canceled for the first time since World War II and the French Open moved from May to Sept. 20. The next major is the U.S. Open, scheduled to begin Aug. 31 in New York.

There are practical reasons for Federer's decision, too. The French Open's clay courts aren't a favorable surface for him and the heat of New York has been a problem, too. In addition, the game's biggest players have indicated that they have concerns about traveling during the pandemic.

If a vaccine were available, players are at odds over whether they would take it if required by the Association of Tennis Professionals. Djokovic initially said he was against it, but said he was open to considering it. Rafael Nadal said players would have to follow whatever the rules are no matter who they are.

"Djokovic will have to be vaccinated if he wants to keep playing tennis at the top level," Nadal said recently. "The same for me. Everyone will have to follow the rules, just like now we have to stay at home. . . . If the ATP or the International Tennis Federation obligates us to take the vaccine to play tennis, then we will have to do it."

When tennis resumes, it may look drastically different, at least at the moment. Initial plans for the U.S. Open call for no fans in the stands and charter flights to carry players and limited entourages from Europe, South America and the Middle East to New York, The Associated Press reported. Players must test negative for the virus, housing would be centralized and there would be daily temperature checks. In addition, there would be no locker-room access on practice days and there would be fewer on-court officials. The situation for now is "still fluid," a USTA official told the AP.

And, with Federer out, there is the sobering possibility that the U.S. Open men's draw could be missing three of the game's top players.

Djokovic, who said he is thinking of skipping the U.S. Open to prepare for the French, calls the possibilities "really extreme" and Nadal last week seemed unlikely to come to New York.

"Today," Nadal said, "I will say, 'No.' In a couple of months? I don't know."