Whitlock was unavailable for Wednesday's game against the Blue Jays due to elbow inflammation, Chris Cotillo of MassLive.com reports.
Interim manager Chad Tracy said after the game that Whitlock has been dealing with a nagging elbow issue for a while. The 30-year-old right-hander is scheduled to undergo further evaluation Thursday, at which point the team may know whether he has to spend time on the injured list.