Serena Williams tweets photo of severely swollen ankle

We can only assume this is what it appears to be -- the right ankle of Serena Williams.

https://twitter.com/serenawilliams/status/294294580608790529

Williams collapsed to the court with an ankle injury in her first-round win at the Australian Open and then appeared to aggravate it in doubles the day before her quarterfinal match with Sloane Stephens.

In that 3-6, 7-5, 6-4 loss to Stephens, Williams called a medical timeout due to back spasms, possibly brought on by overcompensating from the ankle injury.