Former world number one Roger Federer is not ready to concede the French Open will be a straight fight between Novak Djokovic and Rafael Nadal.
Djokovic has put together a run of 32 consecutive wins this year, while Nadal is a five-time winner of the Roland Garros tournament.
Federer, Djokovic and Nadal are sharpening up their preparations for the French Open at the Rome Masters.
And Federer said: "The other players are right behind waiting to strike."
Many in the tennis world feel the once dominant Federer, a winner of 16 Grand Slam titles, is a fading force, particularly on clay. But the 29-year-old from Switzerland does not see it that way.
He said: "It's definitely an interesting time right now that Novak hasn't lost all season long. It makes it a new, different situation, but for me it doesn't change a whole lot.
"Right now [Djokovic and Nadal] are playing better than me and better than other players. I feel like everybody can play on all the surfaces these days and that makes it extremely hard to win all these big tournaments."
Federer was buoyed by taking a set off Nadal in the semi-finals of the Madrid Masters, and said: "I again was really close up against Rafa and so all I need to do is to get that step further and I hope I will do that this week."
Federer's first opponent in Rome on Wednesday will be former Australian Open runner-up Jo-Wilfried Tsonga. Nadal opens against either Italian qualifier Paolo Lorenzi or Brazil's Thomaz Bellucci, who reached the Madrid semi-finals before losing to Djokovic.
Djokovic starts off against Polish qualifier Lukasz Kubot.
Meanwhile, Juan Martin del Potro is a doubt for the French Open, starting on 22 May, after revealing he has a torn hip muscle.
The former US Open winner pulled out of last week's Madrid Masters and has undergone tests on his injury.
"The results of my tests showed a tear in the hip," the Argentine wrote on his Twitter page.
"I have already started rehabilitation and I will do all I can to be in Paris."
Del Potro, who reached the semi-finals at Roland Garros two years ago, has been beset by injury in recent times and missed most of last year with a wrist complaint.