Roger Federer reveals he injured himself while preparing bath for his twin daughters

Swiss tennis ace Roger Federer has said he suffered a knee injury in January while preparing a bath for his twin daughters.

The 17-time Grand Slam winner needed arthroscopic surgery and has made a return at the Miami Open this week.

"I was going to run a bath for the girls. I made a very simple movement, turned back, heard a click in my knee. I went to the zoo. My leg was swollen," Federer was quoted as saying by BBC on Thursday.

The 34-year-old said he was disappointed that he had to undergo an operation.

"I thought I was going to get through my career without any. It was a big shock and, yeah, disappointing," said the Swiss, who is set to lock horns against Argentina's Juan Martin del Potro in Round 2 here.