Federer will go for a fourth straight Grand Slam title in Paris

The current holder of the Wimbledon, US Open and Australian Open titles can complete the set at Roland Garros.

But having started that run in SW19 last June, would it be a Grand Slam as it will not be within a calendar year?

Former French Open champion and world number one, Thomas Muster, told BBC Sport: "For me the Grand Slam is to win it one year."

And Muster, who will play on the Merrill Lynch Tour of Champions in Rome next week, is not keen to join the rush of people already proclaiming Federer as the best male player of all time.

It's going to take a lot for Roger to win it Thomas Muster

"If he does it, he'll certainly be up there with all the others, but I have a problem with mixing generations," said Muster.

"I don't think it's fair. You could talk about Rod Laver being the best, Pete Sampras being the best, John McEnroe being the best and Roger in different generations.

"They've all been great players using different racquets in different generations. He's already the best player of his generation, but I don't like to say who is the best ever.

"If you ask 10 different people, you will get 10 different opinions."

All talk of a Grand Slam would be academic if Federer were to fail at Roland Garros, and with defending champion Rafael Nadal in his way the Swiss faces a mighty challenge.

"He is capable, but he has the same problem as Pete Sampras had," said Muster.

"He's got to play two solid weeks, he's got to survive against all the Spanish and Argentine players, he's got to have a couple of rainy days in a two-week French Open and it's going to take a lot for Roger to win it.

"He could, but I think it's the most difficult of all the Slams to win.