"He didn't come out very good from his 'pen," manager Don Mattingly said. "He felt a little grab in there again. So, we're going to slow him down, and I think he's going to talk with Dr. Kaplan again and see where it goes."
Dunn opened the season on the disabled list, retroactive to March 25, which meant the earliest he could have been reinstated was this past Saturday. However, the initial hope was he would miss the first road trip and be ready for when the Marlins open a series on Friday against the Braves.
Right now, there is no timetable for a return.
"They kind of said he's going to be down a few days," Mattingly said. "We'll find out once he talks to the doctor, and we'll go from there. So not great news for him."
An initial MRI didn't show any structural damage. But the 30-year-old southpaw has some inflammation, and the club is being cautious about rushing him back.
Dunn has been one of the most durable and dependable Marlins relievers in club history. Since being obtained from the Braves as part of the Dan Uggla trade in 2011, Dunn has appeared in 354 games, second only to Braden Looper's 368.
Piecing together the bullpen has been a challenge for Mattingly. The club was already dealing without Carter Capps, who had Tommy John surgery early in Spring Training.
"We've started the season like this," Mattingly said. "Obviously, Mike is a guy we're counting on. We're just not going to be able to count on him yet.
"We'll use a combination of guys. We'll just have to use a combination of guys back there."
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.