The defender joined Die Konigsblauen on a season-long deal in August 2016 but saw his spell cut short by a serious knee injury which has kept him out for the last year.
With his Chelsea future looking bleak, a return to the Bundesliga, where the Ghanaian also played for Augsburg, has been mooted.
Schalke have been mentioned as an option and Heidel says the clubs have spoken and a deal could be on the cards.
He told his club's official Twitter site: "We're in talks with Chelsea regarding Baba Rahman. There are still one or two things to clear up on their end.
"We could agree on a deal with the player himself relatively quickly."