Prior to the ATP Tour going on hiatus due to the coronavirus pandemic, Federer underwent knee surgery in February and ruled himself out of the clay-court swing.

With Wimbledon cancelled due to the proliferation of COVID-19, tennis will not return until mid-July at the earliest and Federer said the extended break means there is no rush in his recovery.

"I've been hitting it a little bit against the wall," Federer said. 

"Rehab with the knee. It's okay. I had a really good first six weeks, then it was a bit slower, now it's getting better again, but I have plenty of time.

"So there is no stress, no rush, if there's anything positive, that's the only thing really. At the end of the day I just want the knee to be good, it doesn't matter when I return.

"I feel happy. I think after the second surgery. It's easier the second time around, but I don't need to experience a third one, that's for sure."

Murray has played just one competitive match since winning the European Open in October, a remarkable achievement after the Briton underwent hip resurfacing surgery.

The three-time grand slam winner will reassess how soon he can be back on the practice courts when the global health situation improves.

"It's good. I've been training a lot," Murray said.

"I'm still able to do lots of things but I haven't practised for five weeks, since everything started to get shut down here.

"So I've not hit any balls but I'm still doing lots of training and I feel pretty good so we'll see what happens when we're able to start doing things again."

When Federer had the chance to quiz Nadal a little, he asked the Spaniard about the origins of him playing left handed when it has always been said he could play with his right.

"That's just a legend. I can write with the right hand, my basketball skills are with the right, but not in the tennis court and not in football," Nadal replied.

"I started with two hands, backhand and forehand. So probably the people, because I was hitting two backhands, didn't know whether I was lefty or righty."

Murray and Nadal also exchanged memories of playing games consoles with one another, with the pair signed up to play a virtual Madrid Open starting on April 27.

With the two attempting to organise a practice session for Monday, Murray said: "I'm up for that, for sure, just not too late because I have to get up with the kids in the morning.

"I'm 6am every morning the kids are getting us up so enjoy your late nights and your lie-ins whilst you don't have kids!"

Nadal replied: "I hope to be in your situation in a not very long period of time."