The Ghana international made 21 appearances for the Bundesliga side last term before he sustained a season-ending knee injury on international duty in January.
Schalke sporting director Christian Heidel has now revealed they are considering bringing Rahman back for another loan stint, although any deal depends on the 23-year-old's recovery.
"We are in talks with the player, his agent and Chelsea," Heidel told Schalke's official website.
"Ultimately, it is about when Baba will be able to play again. No decision has been made yet."
Heidel claims Schalke's business for the summer is all but over, regardless of whether or not Rahman returns, but he would not completely rule out further additions.
He added: "Nothing is planned, but you should never say never in football.
"I do not know what will happen tomorrow, the day after or next week. The fact is a transfer is possible until August 31, but our squad is very good in terms of quality and depth."