Spring Training is not starting out well for the A's so far this season. From Jane Lee:

Less than an hour into their first full-squad workouts of the spring, the A’s suffered what could potentially be a big blow to their infield, as Scott Sizemore went down during an infield drill with an apparent left knee injury and exited the field while applying no weight on it at all. It’s obviously too early to speculate how serious the injury is, but I heard several players mentioning they heard Sizemore’s knee "pop" — which, you can imagine, is never a good thing. We’re waiting to hear more details from manager Bob Melvin shortly.

Brooke Sizemore, Scott's wife, tweeted that he will have an MRI tomorrow.

We are obviously thinking good thoughts for both of them. The A's cannot afford to lose any of their already-thin infield.