"It's not the break that we needed, for sure," Redmond said. "It's a fluke deal, a foul tip. It just hit him perfect."
The injury occurred in the top of the fourth inning of Miami's 8-3 win over the Cardinals at Roger Dean Stadium.
Mathis was clipped by Matt Holliday's foul tip. Initially, he shook it off and remained in the game for one more pitch. But after Holliday drew a walk, Mathis felt discomfort while throwing the ball back to pitcher Brad Hand.
"When I went to throw I felt it," Mathis said. "It wasn't right. Right now, it's non-displaced, which is good.
"I've had a broken face, broken hand, and broke wrist. I've never messed my collarbone up."
Mathis likely will not be ready for Opening Day on April 1 at Washington. The 29-year-old last was on the disabled list in June 2010, when he was out with a fractured right wrist. He was with the Angels at the time.
The Marlins obtained Mathis from the Blue Jays in November, and the club has been counting on him to back up Rob Brantly.
Miami already is thin on catching depth.
"He is going to play a leadership role, for sure," Redmond said about Mathis.
Kyle Skipworth replaced Mathis in the fourth inning. Jake Jefferies is another candidate. Wilfredo Gimenez and J.T. Realmuto, two prospects, are the other catchers in camp.
"I feel bad for us, but bad for him," Redmond said. "He was excited. He's been great around the young guys. We just have to figure it out tomorrow and see where we go from here."
Redmond is a former catcher who retired after the 2010 season.
Would the 41-year-old, who last played for the Indians, consider a player/manager role?
"I don't know. I don't think so," Redmond said, laughing. "I like the way my body feels right now, the way it is."
Cardinals manager Mike Matheny, also a former catcher, was stunned that Mathis suffered a fracture on what appeared to be a routine foul tip.
"That's a shame," Matheny said. "It looked like it got him good, but it's hard to believe a broken collarbone on a foul ball. Everybody thinks catchers are back there suited in armor. It protects your heart and protects your face, but there's not that much to it."
It's been a physically taxing start to Spring Training for the Marlins.
On Monday, first baseman Casey Kotchman sliced his left ring finger and received four stitches after colliding with the machine that shoots out pop ups. Two days later, Giancarlo Stanton was struck in the back of the head by a Jose Fernandez fastball in a simulated game. Stanton, fortunately, is fine, and he played on Saturday, driving in two runs.
In recent days, the team also learned that first baseman Logan Morrison will not be ready for Opening Day. Morrison is recovering from right knee surgery, and just this week was cleared to begin running on an anti-gravity treadmill.
If there is good news, Mathis' injury occurred five weeks before Opening Day.
"It doesn't look like it's a season-end-type situation, which is good," Redmond said.
In the past, Mathis said he has broken several bones, but never his collarbone. The impact of the foul tip went through his chest protector.
"It hit me in the pad," Mathis said. "It was just one of those things, where it catches you right. I've been hit there a lot of times.
"It felt like any other foul tip, I'd taken off the mask, the shoulder, the hand. When I went to throw, I knew it was something."