As organizers finalized plans to move the Australian Open to February from its usual January start, the top 100 men and women in the world rushed to sign up, yearning to play a Grand Slam in a country with few cases of the coronavirus, even if it meant a two-week quarantine upon arrival.

Then, just days after signing on, Roger Federer announced Monday he would not play in Australia after all as he works his way back from knee surgeries.

Federer hopes to play again, but will a return take the form of a farewell tour or a legitimate run at championships? Federer turns 40 in August.

He has not played a competitive tournament since the 2020 Australian Open, where he made it through two five-set matches before falling to Novak Djokovic, the eight-time champion, in the semifinals. He also played a charity match in South Africa in February, but he announced early during the pandemic that he would shut down for the rest of the season as the sport itself was working out when it might return.

As he recovered in Switzerland from his first knee surgery during the initial lockdown, Federer charmed fans by hitting in the snow outside his house. Then came his announcement that he’d had a second surgery in the spring, and he spoke of his slow recovery.

“I’ve had two knee surgeries, so it has been dominated by that — by rehabbing, being on crutches, recovering from the surgery and taking it step by step. I must say I feel much better already again,” he said during a sponsor appearance last summer.

As expected, he skipped the United States Open and the French Open. Tennis inched toward its next phase, as Dominic Thiem and Alexander Zverev battled in the U.S. Open final to become the first new men’s Grand Slam winner since 2014, with Thiem coming out on top. (Rafael Nadal skipped the tournament to avoid traveling to the U.S., and Djokovic was ejected for swatting a ball that hit a line judge.)

Nadal tied Federer with his 20th Grand Slam at the French Open in October.

Federer remained hopeful that he might be able to appear in Australia, especially after it became clear that the tournament would be pushed back three weeks to accommodate strict protocols for international travelers, including players.

But in a statement to The Associated Press, Tony Godsick, Federer’s agent, said Federer had decided that despite recent progress, his best chance for success in whatever time he has left in professional tennis would be to return after the Australian Open.

“I will start discussions this coming week for tournaments that begin in late February and then start to build a schedule for the rest of the year,” Godsick said.

That could include plans for the Olympics, where Federer won a gold medal in doubles in 2008 and a silver in singles in 2012.

In a statement, Craig Tiley, the Australian Open tournament director, said: “The Australian Open has always held a special place in his heart — remember it was Roger who first called the Australian Open the ‘happy slam’.”

Federer is still the world No. 5. He last won the Australian Open in 2018 at 37. It is his most recent Grand Slam title. After he nearly won Wimbledon in 2019, it seemed as though he might be able to compete at the highest level for several more years.

Now it is unclear when he might come back, much less contend against his longtime rivals, Djokovic and Nadal.