McLaren driver Lewis Hamilton has been heavily linked with a switch to Mercedes for the 2013 campaign, but Brawn insists that Schumacher is 'very involved' in the decision to either continue in the sport or signal a second retirement.
"It is still under discussion, I'm afraid," Brawn explained to BBC Radio 5 live. "I can't comment very much on that, but Michael's been a huge asset to the team. He's really taken us forward.
"I do think Michael contributes an awful lot, so I think the decision for Michael to stay or not continue is a difficult one. Obviously he's very involved in that decision, and discussions are ongoing at the moment."
Brawn was later pushed on the possibility of Hamilton moving to Mercedes, admitting that the former title winner is a target for any 'ambitious' outfit.
"He's a very good driver, a very good driver," Brawn added of Hamilton's capabilities.
"Any ambitious team looks at the top drivers and we're an ambitious team, but I think there's an awful lot of speculation. We will have some things to say in the next few weeks, next few months, and then all will become clear."