Which Starlet's Leg Got Banged Up?

Duh, it's Karina Smirnoff.

The Dancing Star proved she's been in the studio whipping her new dance partner (and herself) back into shape for the upcoming DWTS season, which debuts Sep. 22nd. 

But while the starlet walked into Kress Nightclub looking confident and happy, her expression had turned to shock by the time she headed home...

Did someone accidentally or on purpose spill the beans about her on-again boyfriend Mario Lopez's latest infidelities?