Baker suffered a similar injury playing against the Giants on May 9.
"Yeah, he did it in that at-bat. Guess it's similar to what he did out in San Francisco," Jennings said. "It grabbed him pretty good."
Baker, hitting .208 in 41 games this year, has played almost exclusively at first base for the Marlins. With Michael Morse and Justin Bour in the fold, however, the team should be well-equipped to cover for his absence once it returns to a National League ballpark.
"It's just going to be one of these day-by-day type deals for right now," Jennings said. "We'll know a little more as he starts to move and see exactly how long it's going to be."
• Martin Prado, on rehab assignment after suffering a right shoulder sprain, played his second game as the designated hitter for Class A Advanced Jupiter on Wednesday night and lined a single to center in his first at-bat. He went 1-for-4 with a run scored as the DH on Tuesday.
Prado will not play third base until Saturday at the earliest, when he would likely join either Double-A Jacksonville or Triple-A New Orleans. The team expects him to return after the All-Star break.
• The Marlins will re-slot right-hander David Phelps into their rotation for Friday night's game against Cincinnati. Phelps, who pitched 4 1/3 scoreless innings across two appearances as a long reliever, has not started a game since allowing five runs over 5 2/3 innings against the Reds on June 21. He is 4-4 with a 3.84 ERA in 13 starts this season.
"He's done the job, he's stretched out," Jennings said. "That's big, the fact that he is stretched out and can jump back in there. We knew Phelpsy had that versatility that he could come out of the bullpen in a short spurt or he could give you multiple innings or he could start. Having a couple guys like that's huge, because they have the ability to make pitches and throw strikes, no matter what role. And that just speaks to the type of team player he is."
• With Miami scoring four or fewer runs in 14 of its last 18 games, the team held a hitters-only meeting prior to Wednesday night's game at Fenway Park.
"Just make sure we feel good. Gotta feel good to play good," Jennings said.