"We'll re-evaluate in the morning," said manager John Farrell. "He'll likely go through an MRI just to determine what's going on. We don't have a roster move right now."
Doubront, who was the losing pitcher in Toronto's 7-4 victory over Boston, is unsure if the injury is serious.
"We'll just wait until tomorrow to see what kind of tightness is there," said Doubront. "I felt fine during the game. Right now, I feel fine. During the game, I couldn't feel my shoulder. Weird. It felt weird."
Doubront gave up five hits and five runs over four-plus innings of work, walking three, striking out two and giving up two home runs.
He threw 65 pitches, 40 for strikes.
"The more I threw -- I started feeling it the second inning, when I walked [Dioner] Navarro. I noticed that I wasn't feeling the grip in my hand. I started feeling that, the more I threw."
If Doubront is forced to miss a turn in the rotation, the Red Sox will need to find a replacement for Sunday's game against the Rays.
The lefty is 2-4 with a 5.12 ERA this season.
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.