Federer defeats Rochus in 3 sets, but what's on his face?

Roger Federer struggled to beat Olivier Rochus in the first round of Estoril, needing 3 sets to put away the diminutive Belgian.

But what is the large bump on the side of Fed's face? It looks pretty swollen, like a bee sting or something.

Strange...

*VIA DOWNTHELINETENNIS.COM

(images via AP)