Furcal is sidelined with a strained right groin, an injury he first incurred a week ago, and was again aggravated while playing for Double-A Jacksonville on Friday night.
"I think he wants to play so badly that he probably is pushing it before it's 100 percent," Marlins general manager Dan Jennings said. "In doing it, you run that risk."
Furcal opened the season on the disabled list with a left hamstring strain. But at Jacksonville, he aggravated his groin on April 25, leading to him being returned from his first rehab assignment two days later.
Miami sent Furcal back out for his second rehab assignment, which began Friday.
The Marlins signed Furcal to be their regular second baseman, but he has been on the disabled list all season.
For now, the team wants him to get healthy, and not push a return date.
"At 36, and being that veteran player, you've got to lean on him some in that decision process," Jennings said. "In his desire to come back, he's probably stretched himself a little more than he needs to."
Joe Frisaro is a reporter for MLB.com. He writes a blog, called The Fish Pond. Follow him on Twitter