Former World No. 1 Roger Federer has withdrawn from the National Bank Open Presented by Rogers in Toronto and the Western & Southern Open in Cincinnati due to a knee injury, the ATP Masters 1000 tournaments announced Thursday.

The 39-year-old underwent two right knee surgeries in 2020 after the Australian Open before returning to the Tour in Doha this March. Federer has competed in five tournaments this year, recently missing the Tokyo Olympics due to injury.

When he announced his withdrawal from the Olympics, Federer tweeted: “During the grass-court season, I unfortunately experienced a setback with my knee.”

The World No. 9’s best result this season was a run to the Wimbledon quarter-finals. The 28-time Masters 1000 champion also competed at Roland Garros, where he reached the fourth round before withdrawing. Federer has enjoyed success in Canada, winning two titles in Toronto, and is a record-holding seven-time champion in Cincinnati.

It was also announced Thursday that Tokyo Olympics singles gold medallist Alexander Zverev will not compete in Toronto.

“I regret to inform you that, unfortunately, I have to withdraw from the National Bank Open in Toronto,” Zverev said in a statement. “Due to the intense past couple of weeks and my incredible experience at the Olympics, I need to recover so that I can hopefully be at my best for the remainder of the U.S. summer swing. It was a difficult decision for me as I have had great memories from Canada and I can’t wait to be back next year!”

Italian Matteo Berrettini, Canadian Milos Raonic and Spaniard Pablo Carreno Busta have also withdrawn from Toronto.