The Athletics have shut down outfielder Stephen Piscotty after an MRI revealed an intercostal strain.
Oakland manager Bob Melvin said the tests were "a little worse" than the team expected and acknowledged that Piscotty could miss Opening Day.
"I can't give you a timetable at this point," Melvin told reporters Friday.
Piscotty, 29, has yet to play this spring for Oakland due to the injury.
He hit 27 home runs in his first season with the A's in 2018, but injuries kept him to just 93 games last year.
Athletics shut down Stephen Piscotty with intercostal strain