LONDON (AP) — South African tennis player Kevin Anderson has had surgery on his right knee and will be out for an unspecified period of time.

The two-time Grand Slam finalist wrote on Twitter on Friday that he had surgery Wednesday on a torn meniscus.

Anderson said he injured his knee in December and tried to play through the problem at the start of the 2020 season, including at the Australian Open. That was after his 2019 season was disrupted by injuries, including an elbow problem which forced him to miss the clay-court season and a knee injury which kept him out of the U.S. Open.

“It is beyond difficult and frustrating to have to deal with this, after the setbacks I had last year,” Anderson wrote. “But I know it's the right decision for me to get back where I want to, and rest assured I will do everything in my power to get there.”

Anderson's ranking has slipped to 121st following a second-round exit at the Australian Open. He last played in New York last week, when he lost to Jason Jung in the first round.