Serena Williams won't rush back after battling injuries in 2016

Serena Williams says she's sick and tired of playing top-level tennis while injured.

The 22-time grand slam champion lost her world No. 1 ranking to Angelique Kerber this month when she was

Williams has struggled with injury over the past year, with shoulder and knee problems increasing her frustration throughout the season.

And the American -- who turns 35 next week -- is refusing to put a date on a comeback, instead focusing on making sure she's close to full fitness before making a return.

"I'm tired of playing tournaments unhealthy and taking losses that I would never lose," Williams told CNN at the unveiling of her French coach Patrick Mouratoglou's new tennis academy near Nice.

"I definitely want to make sure I'm healthy and playing at my best or at least 80% healthy or 70% healthy -- that way I can be able to play at a higher level."

The knee injury appeared to play a significant part in Williams' shock defeat by in the last four at Flushing Meadows.

While she refused to blame the injury for the loss, the result meant she managed to land just one grand slam title compared to the three she won a year earlier.

Williams has three tournaments  Two in China, then the season-ending WTA Championships in Singapore starting October 24. She missed the tour's Asian swing last year due to injuries.We have to be honest -- it has been a bad season for her," he told CNN. "She's been injured a lot, which makes it worse because she couldn't play much.

"She played only eight tournaments, which is really, really, not much. For Serena, any result that is not a title is a bad result -- so a final of a grand slam is a bad result for her. We can't be satisfied with one grand slam final and two finals lost.

"It's a bad year, there are many explanations but we have to learn and be better next year and that is definitely the goal. This is not satisfying at all."