St James Leisure Centre is temporarily closed due to structural problems.
The incident concerning the gym roof happened on Tuesday, no one was injured.
Michael Hart, chief executive, of Doncaster Culture and Leisure Trust said: “We have temporarily closed St James Leisure Centre after the building sustained structural damage on April 9.
“While no one was injured we believe that this currently poses a health and safety risk and for the protection of our staff and the public the venue will remain closed until the damage has been assessed.
“Experts have been called and will visit the site this week to give their opinion on suitable next steps.”
During the closure, members will be will be free to use any other DCLT facilities. All other customers will be offered a 7-day pass to use other DCLT facilities and can speak to a member of staff for details.