Schalke have been dealt a blow after Ibrahim Afellay suffered yet another injury setback.
The Netherlands international has been out of action ever since he picked up a hamstring problem back in November while away on international duty, but he recently resumed regular training action again.
However, the Barcelona loanee, 26, has endured a setback at Schalke's training camp in Dubai and is in severe doubt for the Champions League last-16 clash with Galatasaray next month.
It is not yet known exactly how long the attacking midfielder will be out of action, but Schalke fear that they will be without Afellay for up to two months.
He joined the club on a one-year loan deal at the start of the season and has since made 15 official appearances for the club, scoring four goals in the process.
Team-mate Christoph Moritz has also returned to Germany after sustaining a medial collateral ligament tear in his right knee during the 3-2 friendly win against Al-Sadd on Sunday.