Stanton underwent an MRI exam Tuesday and said the diagnosis was a grade-two strain on the one-to-three scale for the injury. He was hurt trying to beat out a grounder in Monday's 15-inning victory over the New York Mets, and was placed on the 15-day disabled list.
The injury occurred just as last year's NL slugging leader showed signs of emerging from a prolonged slump to start the season. He hit his first home run Saturday and two more Sunday.
"Awesome timing," Stanton said facetiously. "It's a tough break. Pretty frustrating. It's just one of those freak things. There's never a good time, but this was probably one of the worst times to do it."
Last year Stanton hit 37 home runs despite missing 39 games because of injuries. Now the Marlins, already saddled with the worst record in the majors, will be without their best hitter for several weeks.
"If we could just erase all of April, that would be lovely," Stanton said.
He'll be replaced in right field by 22-year-old Marcell Ozuna, who was recalled from Double-A Jacksonville to make his major-league debut.
"When I received the call, I felt very excited," Ozuna said. "I didn't sleep last night."
With Stanton due to become eligible for arbitration after the season, there's already speculation the thrifty Marlins will trade him, and Ozuna would be the leading replacement candidate.
The Dominican was hitting .333 with five homers and 15 RBIs in 10 games with Jacksonville. He's a career .274 hitter in the minors who hit at least 22 home runs each of the past three seasons.