Clay Buchholz, who has a strained trapezius muscle in his neck, has been placed on the 15-day disabled list.
The Red Sox made the move retroactive to June 9.
Buchholz threw a bullpen session before Tuesday night's game against the Rays, but didn't show enough progress to avoid the DL.
"We didn't feel like we had enough time to give him the proper amount of work to prepare for that start," John Farrell said. "We didn't want to take any chances."
Buchholz will not be eligible to pitch until June 25.
Via Gordon Edes/ESPN