"Even as the day wore on yesterday, some of those spasms began to release a little bit," Farrell said. "Overnight, they were improved gradually once again, but it was clear once we spoke to him this morning he was going to need at least today."
Farrell said "optimistically" Ramirez could return to the lineup Saturday.
Ramirez exited in the fourth inning Thursday, midway through his first game of the season at first base. The veteran is hitting .257 with five home runs and a .773 OPS this season.
Chris Young started at DH Friday in place of Ramirez.
Alex Putterman is a contributor to MLB.com based in Boston. This story was not subject to the approval of Major League Baseball or its clubs.