As far as worst-case scenarios go, this would seem to qualify, as Anthony Andro tweeted out a few minutes ago.

Martin Perez has discomfort in left elbow. Will miss at least one start and have an MRI.

— Anthony Andro (@aandro) May 11, 2014

I can't bring myself to really say much more than this: If this is something serious, it will be a major blow to the Rangers and significantly impact the strategy for the remainder of the season.