Kim Clijsters

MIAMI — Four-time Grand Slam champion Kim Clijsters withdrew Sunday from upcoming tournaments in Miami and Charleston, a setback in her comeback following right knee surgery and a bout with COVID-19.

Clijsters’ return to the WTA Tour in 2020 after a seven-year hiatus was interrupted by the pandemic. She underwent knee surgery in October and came down with a mild case of the virus in January.

"I’ve had an intensive few weeks of training," Clijsters, 37, said on Twitter. "Unfortunately I am not where I need to be, especially if I want to compete with the best. I’m not ready to quit. I’m going to keep pushing and see what’s possible."

Clijsters said she plans to undergo three to six weeks of pain management treatment and then make decisions regarding her schedule.

The Miami Open begins March 23, and the Charleston tournament starts on April 5.