Rafael Nadal will face his biggest test since he returned from his injury-induced layoff in early February. He faces long-time rival Roger Federer on Thursday, and this should serve as a nice between-Grand Slam treat for tennis fans.
The two greats both advanced to the quarterfinals of the BNP Paribas Open and are set to meet for the 29th time in their careers.
Nadal has won 18 of those matches, but their match on Thursday will bring with it a new challenge. Federer is obviously still a formidable opponent, but these days, Nadal battles more than just the man on the other side of the net.
Competing on bum knees creates a new obstacle for Rafa, and with this tournament played on a hard surface, it will be a test for Nadal's durability and game.
Will his knees hold up during and after the match? Will he be hesitant to play his normal baseline game. Since Nadal depends on speed and agility so much to be dominant, the psychological impact of knee problems is no small detail.
Thus far, he has performed well since returning to the court, as he came into the BNP Paribas Open 12-1 through three tournaments this year.
But those tournaments were all played on clay, which is of course Nadal's specialty, and none of the opponents he's faced have been on par with Federer.
More than any other match or moment since he returned, Thursday night's clash with Federer is a measuring stick.
The French Open doesn't start until May, but Nadal's performance in this match is still important. But what is more important than Thursday's result is the level of confidence Nadal has once it's over.
Even if Federer wins, Nadal should at least have a positive feeling about the direction he's moving in as we approach Grand Slam season.