The German club have insisted that their teenage star will not be sold in January, but that has not stopped constant speculation over his future
The 19-year-old has been heavily linked with a move to the Premier League in recent weeks, despite Schalke's insistence that Sane is not for sale at any price.
A number of reports suggest City are preparing an offer in excess of €40million, but Heldt has made it clear there are no developments at this stage.
"There are no offers for Sane at the moment," Heldt was quoted as saying by Kicker.
"It would be wrong not to take any potential developments into account and we are more than experienced enough to realise that.
"But we have also learned that you should not focus on things too much until something becomes serious.
"That is not the case as things stand."
Sane has a contract with Schalke until June 2019.