Third baseman Pablo Sandoval has lower back stiffness and was not in Boston's starting lineup Thursday against the New York Mets.
Sandoval was injured diving for a ball off the bat of Miami's Giancarlo Stanton on Tuesday.
"He is going to be down for a couple of days, just trying to get back to that," Red Sox manager John Farrell said. "So he's going to be unavailable - on a day-to-day status right now.
Farrell said he does not think Sandoval will require a stint on the disabled list.
Sandoval, listed as 5 foot, 11 inches and 255 pounds, appeared to be overweight when he reported for spring training last month. The Red Sox said they were not concerned by his weight and principal owner John Henry said Sandoval's body fat ratio was 17 percent, down from 21 percent last season.
Travis Shaw, one of Boston's prospects, has had a strong spring training, playing first base and third base.