Cosart was on the disabled list in mid-May because of vertigo, and the concern is he has had a relapse. Miami manager Dan Jennings on Saturday said the organization thinks it might be a case of dehydration, but hasn't ruled out anything.
"What the medical report from Triple-A said was that they felt like it was dehydration, electrolytes," Jennings said. "They took him out to make sure.
"He will see the doctor again [Sunday] to rule out anything. Hopefully it was just that. It gets pretty warm in New Orleans. Hopefully it was just that, the dehydration, and nothing connected to the vertigo."
Cosart was lifted after 1 1/3 innings against Colorado Springs.
"He had dizziness on the mound, so they took him out," Jennings said.
It's been a rough season for Cosart, who is 1-4 with a 5.36 ERA in nine games (eight starts) for Miami.
If the issue is vertigo, the organization wants to get a better understanding of why it has returned.
"The vertigo is a very serious illness," Jennings said. "It takes some time. If that is what it is, you want to know what's causing it, and how much down time do you need. I'm sure that will be part of the evaluation of what he gets [Sunday]."
The Marlins acquired Cosart from the Astros last July, and the organization envisions him being a top-of-the-rotation talent.
"It's unfortunate," Jennings said. "We were counting on him to be in that five-man rotation, and certainly towards the top of it. Unfortunately, it's not been a good season for him, due to injury."
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.