"He's a big presence in our clubhouse," Miami manager Dan Jennings said.
Mathis broke his hand on April 12 and went on the DL the following day. He's played in four rehab assignment games for Triple-A New Orleans, going 0-for-10 at the plate.
With New Orleans at Reno on Friday, Miami opted to keep Mathis closer to Florida. So he joined Jacksonville, which is playing at Birmingham, Ala.
Jennings said once Mathis gets in the 15-20 at-bat range, he will be close to being reinstated.
When he returns, Mathis will provide an experienced backup catching option to rookie J.T. Realmuto. Jhonatan Solano currently is the backup.
The Marlins have a crowded DL. First baseman Michael Morse was examined by a hand specialist on Friday. He has a right ring finger strain and could begin swinging the bat in about a week.
Jose Fernandez, recovering from Tommy John surgery, will throw about 45 pitches on Monday in an extended spring game. Jarred Cosart (vertigo) also is scheduled to pitch in the game in Jupiter, Fla.
"You're going to have Cosart and Jose there on the same day," Jennings said. "It's a step towards the right direction for both guys.
"We've got to get guys healthy, get them back. Pitching sets the tone every day. I'm hoping the rehab with some of these guys moves them along quickly, and we can get them up here and they can start to help us."
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter @JoeFrisaro and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.