When I saw his injury I thought "calf strain/tear" immediately, but wanted to reserve judgment. I have struggled with bad calves for almost a decade. The most common way to injure it is just like KG did - a plant and push, without any contact. The injury is quite common among runners, but I hurt mine many times playing hoops.
If it's bad (grade 2 or 3), you feel a "pop" in the back of the leg, and you are done for a few weeks at least. See below for the grades and healing times:
http://orthopedics.about.com/od/sprainsstrains/qt/calfstrain.htmKG is an elite athlete getting the best possible treatment, so maybe the outlook is better for him.
What depresses me about this is that even when you come back, it extremely easy to re-injure. That has its own risks, but also makes you tentative when pushing off with that leg.