Marlins president David Samson announced Tuesday that the franchise has started its search for a new manager. Jennings has not decided whether he will return to the team, according to president of baseball operations Michael Hill.
Jennings made the unusual move from GM to manager when the Marlins fired Mike Redmond in May after a 16-22 start.
The change failed to spark a turnaround, and the injury-riddled Marlins finished at 71-91, their sixth consecutive losing season.
Jennings has been with the Marlins since 2002 and is under contract through 2018.
Information from The Associated Press was used in this report.