Who are Nadal's biggest threats on clay?

This is a question that probably bugs a lot of tennis fans, since practically no one can get in this guy's head and beat him on his best surface. But there are a few players good enough to give him some trouble and I'm thinking Gulbis has now joined this club.

It seems like the tall, hard hitting, aggressive baseliners are the players that Nadal, struggles with most. Over the past year he's faced Soderling, Del Potro, Djokovic, yeah, I'll throw in Davydenko and they've all given him problems, even on clay. If Nadal were, to lose the French Open this year, then my guess, is that it would be to one of these powerful baseliners and not to Roger Federer.

Lately, there's been two different Roger Federers, on tour. The Roger, who plays in the masters series and the Roger, who plays the majors. They're both strikingly different. Masters Series Roger, has an error ridden game and is prone to losing in the early rounds of tournaments. Grand Slam Roger, is a great player who sometimes struggles, in the early rounds but usually finds, his best game and simply confounds his opponents, with incredible shot making.

Grand Slam Roger, is a serious threat to Nadal but he's still at a disadvantage because his game relies on timing, where as Nadal's does not. Even if Roger comes at Nadal with everything he's got, Nadal will probably still win the match. Roger's backhand has been his Achilles heel and Nadal knows that he just has to work it over until the errors start surfacing in Federer's game. Nadal is just a bad match-up for Roger, especially on clay.

Finally, there is one more player that I wanted to talk about, Thomas Berdych. Berdych, is a tall guy with a huge serve, excellent ground strokes, good consistency, and pretty solid movement. On paper he has all of the tools needed to beat Nadal and he's even had some success again him, although it's mostly been on hard courts. I think Berdych can beat Nadal, but I'm not sure if he believes he can do it. Berdych, has a reputation for not staying focused throughout matches and for blowing leads (like in the 2009 Australian Open, when he lost to Federer, after being up 2 sets to love.) In my opinion, Berdych needs to come to the French Open, focused and ready to blow Rafa off the court and if he does everything right, while keeping his focus, he stands a great chance to force the upset.