Roger Federer labelled Serena Williams arguably the greatest player of all-time.

The world number two is currently skipping the clay-court season before preparing for a strong second half of the year.

Williams is preparing to play at the French Open – her first grand slam since having her first child – and is looking to add to her 23 major singles titles.

Federer is two months older than Williams and both have enjoyed similar success, but he reflected on the different paths they had taken.

"She had a totally different upbringing – I came up through Switzerland with the federation, she did it with her dad and her sister," he said.

"It's an amazing story unto itself and then she became one of the greatest, if not the greatest tennis player of all time."

He added: "We know [Williams] is all the way up there. I’m probably up there with somebody, somehow. Maybe there's a group, a best of five, and if you're in that group, you should be pleased and happy."