The official statement from the Red Sox crack medical team stated that Josh Beckett's injury was "consistent with an ankle sprain." Of course, given the events of the last year or so, the credibility of this statement is roughly on the same level as one issued by Mahmoud Ahmadinejad.
Beckett's own comments in the immediate wake of the injury are still scary—essentially saying something "popped" out of place when he fell in the Toronto bullpen during pre-game warmups. Popping in the ankle is never a good thing—ask Curt Schilling.
We can only hope that Doctors Howard, Fine and Howard are correct this time, and Josh will only miss one or two starts.