Check this out:
http://tt.tennis-warehouse.com/showthread.php?t=309722
"Federer was crushed in the first set and then took a bathroom break.
After the match, he explained why:
"When the sun comes from the side, the ball seems half the size and is just hard to hit. I never take toilet breaks, but I thought 'Why not?'
I just hoped that with every minute it took, the sun would move another centimeter."
He then threw in, as an afterthought, that he also had to go to the bathroom.
Well, tennis doesn't have bathroom monitors. Yet. So we can't say for sure what he did.
But Federer made it clear that he was looking for the break so the sun might set a little and wouldn't be in his eyes. And the rules clearly state that a bathroom break "can be used for no other purpose" than going to the bathroom.
A few minutes after Federer returned, Davydenko fell to pieces."