Jarrod Dyson can still run, but throwing is out for a while.
A MRI exam Friday detected that the Kansas City Royals outfielder has a strained right latissimus dorsi muscle.
"That's what it shows," manager Ned Yost said. "We'll shut him down from throwing."
Dyson said he believes the injury occurred Monday when he banged into the Fenway Park wall while making a catch.
"I didn't feel a thing, but I kind of felt a little tightness on Tuesday," Dyson said. "On Wednesday, I really felt it. Right now, it's just day-to-day. It depends on how I feel. I'm still available to run."
He said it hurts a little bit when he throws.
"It doesn't bother me swinging," Dyson said. "It's not major-major, just a little soreness in there."
Yost said the Royals do not have to put Dyson on the disabled list with major league rosters eligible to be expanded from 25 to 40 beginning Saturday. He said the Royals would probably promote an outfielder from the minors.
Yost said Dyson, who has 25 stolen bases in 28 bases, is still available to pinch-run.