Schalke expect midfielder Leon Goretzka to announce whether or not he will sign a new contract before the end of January, Clemens Tonnies has said.
The Germany international's deal expires at the end of the season and he has been heavily linked with a move to Bayern Munich.
Bayern head coach Jupp Heynckes admitted this week he is a fan of the 22-year-old, before sporting director Hasan Salihamidzic confirmed the Bundesliga champions were interested in signing him, prompting Schalke sporting director Christian Heidel to issue a strong rebuke.
Tonnies, the chairman of Schalke's supervisory board, says they have done everything to convince Goretzka to sign a new and improved deal and has urged the player to tell the club of his plans soon.
"We've done everything to ensure he stays," Tonnies told Welt am Sonntag. "In January, he wants to say what he's doing.
"Schalke have accepted the financial conditions of Leon and his management. He was also important for the sporting development of the team last summer and, after the first half of the season, we're in second place and in the quarter-finals of the DFB-Pokal.
"Leon can and must decide now."
Tonnies thinks Goretzka could benefit from rejecting a move away this year in order to develop into a better player before a possible transfer in future.
"I firmly believe Leon Goretzka could have incredible development at Schalke. We're not blocking his way to an even bigger club in a few years," he said.
"I think he would be fine if he stayed."
Goretzka is the latest star of Schalke's impressive production line, which has given the likes of Mesut Ozil, Manuel Neuer and Leroy Sane their breakthroughs in senior football over recent years.
"This shows the excellent youth work we do," said Tonnies. "However, it also means players like that arouse the interest of even bigger clubs. Unfortunately, that's the way things are going.
"There are clubs in England, Spain, plus Bayern, which are more attractive for good, young players. We have to admit that."