Schalke have suffered a double injury blow with the news Albert Streit and Gustavo Varela could miss the start of the season.
Midfield duo Streit and Varela both picked up knocks during the club's 4-1 friendly win over the Bahrain national team on Tuesday.
Streit, who came off after 30 minutes, faces at least a fortnight on the sidelines after tearing his thigh muscle, while Varela's recovery time is not yet known after he limped out of the game at half-time with a groin problem.
Both will commence rehabilitation with physiotherapy at Schalke's training camp in Austria, but are doubts for the start of the Bundesliga season.
The injuries are a further blow to the Royal Blues, who have already seen Brazilian full-back Rafinha depart without permission to the Olympics.
Schalke's kick off the new campaign with a trip to Homburg on August 8 in the first round of the DFB-Pokal.
Their first league match is seven days later when they take on Hannover at the Arena AufSchalke.