The centre-back - nicknamed The BFG by Gunners fans - moved to the Emirates in 2010 from Werder Bremen, having previously spent 11 years with Hannover at academy and first-team level.
Hannover found themselves relegated from the Bundesliga at the end of last term, and Bader believes that the club will need to bounce back to the top flight before they can think about offering the 32-year-old a return to the HDI-Arena.
"Everybody knows what Hannover mean to Per. Maybe we can make him enthusiastic about a return," he said.
"But re-signing Mertesacker is not our main priority at the moment. We are playing in the 2. Bundesliga right now and he is Arsenal's captain. A lot of things will have to happen in order to make a return a realistic option.
"First of all, Hannover will have to return to the Bundesliga. A transfer is still far away now and it seems like a crazy thing to even discuss it. But anything can happen in football."
Mertesacker's current contract with Arsenal expires at the end of this season.