Roger Federer, not known for serious slip-ups in his flowing run to a record 17 grand slam singles titles, has come clean about the left knee injury that sidelined him for nearly two months.

The Swiss maestro, who will resume competition at the Miami Open on Friday, revealed that he tore the meniscus in his knee when he slipped while running a bath for his twin daughters in Melbourne, following his semi-final loss at the Australian Open.

The 34-year-old Federer told reporters he felt a "click" as he transferred his weight to his left leg, but did not realise the seriousness of the injury at the time.

It was only later, after returning home to Switzerland, that an MRI revealed the extent of the injury and prompted arthroscopic surgery on February 3.

"I remember I turned, I felt my knee was funny, I turned back. That's when I heard a click," Federer said.

"I did feel that something was strange in my knee. Very simple movement, probably a movement I've done a million times in my life for sure.

"When I got the news that I had to have the operation I saw the pictures and talked to my doctor and knew that it was the only way out of this one. In the hospital, when I was about to go into the operating room, that’s when I got nervous and sad about it all."

But the surgery went well, and Federer, after 12 days on crutches, was able to resume training and is now ready to resume his 2016 campaign.

Federer will be tested straight away as his first opponent will be Argentine Juan Martin del Potro, who defeated the Swiss champion in the 2009 US Open final.