Schalke coach fears Draxler exit with Arsenal looming
Draxler was strongly linked with a move to Arsenal last month, despite regular denials from Schalke and Arsene Wenger claiming the rumours were "created by the newspapers," and the German side's sporting director, Horst Heldt, subsequently confirmed a bid from an unnamed club had been rejected.
However, Schalke may be powerless to prevent Draxler departing in the summer. Heldt had recently said that the player's release clause, set at €45.5 million, "was only in place for last year" but Keller has indicated that is not the case.
"I am delighted that we have him on board for the second half of the season but, because of his clause, he can leave when a club puts the money on the table," Keller said. "That's why I can't plan with him, because it is just not in my or our hands."
Keller said he had been concerned that the 20-year-old, who returned to training this week after rupturing his tendon, would leave last month.
"It's a god-awful situation when, as the coach, you don't know whether such an important player will move on, but Julian was injured at that time, so at least any unrest did not necessarily affect the other players," he said.
He also revealed the club had a plan B in mind in the eventuality of a sale, adding: "It would have been bad if we didn't have one. When you have to replace a player like Julian, you had better be prepared."
Draxler is now close to returning to the squad for the first time since mid-December and Keller - who has overseen an upturn in results since the winter break - recognises his importance to the team.
"He's young, but has made over 100 competitive appearances for Schalke," he said. "Others don't achieve that in five, six years. That's why he is very experienced already, and has shown his superior qualities often enough, although his youth shows in his consistency."
Draxler was not at his best in the first half of the season, despite some important goals in Champions League, and Keller suggested the speculation had an adverse effect on his form.
"It's clear that all the talk about his €45.5m release clause and the interest from top European clubs leaves its mark on such a young lad," Keller said. "The hype around him last summer was huge. He must learn to cope with that, and also that failing to perform at less than 100% is not good enough for him."