Stuttgart striker Pavel Pogrebnyak is expected to be unavailable for several months after suffering a knee ligament injury in training.
The Russia international, who has in the past been linked with Sunderland, had just hit a good passage of form and scored in the victory over Hoffenheim earlier in October.
But he is now facing a lengthy period on the sidelines and, with his contract due to expire within 12 months, the injury could cast doubts over his future at Stuttgart.
Pogrebnyak told his club's official website: "It's a blow for me. I have been making strong progress and getting into a good sort of form.
"Now I am out with an injury. That is quite annoying."
Stuttgart manager Bruno Labbadia said: "Pavel Pogrebnyak had been in good form. He showed that in his recent two matches for us in the Bundesliga.
"It's a pity he is now unable to continue with that."