Coghlan, the 2009 NL rookie of the year, was hitting .230 with five homers and 22 RBIs in 65 games this season.
"I really believe and we believe that Chris Coghlan needs to work on his swing," Marlins manager Edwin Rodriguez said. "We all know he's a way better hitter than he's been showing. I think he will be fine. Whenever he's fine, then he can come back here and help us."
Rodriguez said Coghlan took the news hard.
"He knows he belongs here. Just having a bad start," Rodriguez said. "What we've seen from Chris Coghlan, he's going to be the first one to tell you that's not him swinging the bat."
Florida also purchased the contract of outfielder Dewayne Wise from New Orleans as part of a series of moves announced before Friday night's game at Tampa Bay.
"I feel very comfortable putting him into the starting lineup," Rodriguez said. "He's a good defender and he knows how to handle the bat."
Wise and Emilio Bonifacio will both get playing time in center field.
Left-hander Dustin Richardson was designated for assignment to make room on the 40-man roster for Wise.