To make room for Middlebrooks on the roster, the Red Sox optioned infielder Brock Holt to Triple-A Pawtucket.
Coming off a left calf strain, Middlebrooks went 0-for-4 in his final Minor League rehab game for Pawtucket on Thursday.
"He swung the bat better today," said manager John Farrell. "Came out of it physically fine. I think that's the one thing I talked about a minute ago is just the continuity and some stability with the names we anticipated breaking camp with. Three and a half weeks into the season, we're finally getting there."