The team also optioned lefty reliever Dan Jennings. The Marlins will make a corresponding move on Friday.
Kearns went on the disabled list on May 24, retroactive to May 23, with a strained right hamstring.
Playing for Class A Jupiter on Wednesday night, Kearns was struck on the left elbow by a pitch from Brevard County's Andy Moye.
Thursday was the first day the veteran was eligible to be activated. But because he was plunked on the elbow in his second plate appearance, he was evaluated.
"I think that's kind of what knocked it back a little bit," Kearns said. "We'll wait and see how that is."
Kearns didn't have an X-ray taken.
"I've been hit there many times, not on a rehab assignment, but it's all right," he said.
Kearns has been an important right-handed bat off the bench for the Marlins. He's hitting .375 with three home runs and nine RBIs in 22 games.
The hamstring is improving.
"It's better," he said. "I was moving around all right. We'll just go from here."
By sending down Petersen, who is hitting .212, the Marlins likely will go with Chris Coghlan and Justin Ruggiano in center field until Emilio Bonifacio returns from the DL.
Jennings gave up a three-run homer to Atlanta's Michael Bourn in the ninth inning on Thursday. He has a 1.80 ERA in five innings this season.
Even though sending down Jennings gives the Marlins just one lefty in the bullpen in Randy Choate, the team is expected to recall righty Sandy Rosario, who has a 1.04 ERA in 25 appearances for New Orleans.