Draxler was forced off in Schalke's 1-0 win over Augsburg on Friday after picking up a hamstring injury inside the opening minute, and the German playmaker is facing an extended spell on the treatment table.
"He's picked up another injury," Heldt told the club's official website. "It looks like a serious muscle injury.
"I'm working on the basis that Julian won't play again before the winter break."
Schalke head coach Roberto Di Matteo admitted after the game that losing Draxler to injury is a big blow for his side, who have won three of four games since the Italian arrived at the club last month.