According to Pete Abraham, Felix Doubront is working on his mechanics leading up to his next start.
It's no surprise that the Red Sox think there's a mechanical problem with Doubront, given that his fastball has lost about four miles per hour since the start of the season, now sitting around 89 miles per hour. That decline in velocity, when combined with his typical wildness, has left Doubront entirely ineffective in his last two outings.
Unfortunately, "working on mechanics" all-too-often is code for "completely broken," if not necessarily irreparably so. Quick fixes in these situations are rarely effective, and usually significant retooling time is needed, often in the minors. Of course, with no options left on Doubront, the Red Sox would have to put him on the disabled list to get time to work on him, but given his velocity dip it's not hard to justify such a move.
The problem right now seems to be that there's simply no replacement if the Red Sox don't think Franklin Morales is ready to make the jump back into the rotation just yet. But that doesn't make Doubront any more legitimate an option. Right now he's lost, and throwing him out there time and again hardly seems likely to help him find his way back.