Owen Hargreaves might be forced to miss Bayern Munich's trip to Hertha Berlin on Saturday after he limped out of training on Tuesday.
The England international complained about pain in his ankle after receiving a knock in Bayern's 3-2 UEFA Champions League defeat to Real Madrid last week.
Hargreaves was able to play in the Bundesliga at the weekend, but the problem grew worse and the midfielder was forced to stop training with his team-mates.
Bayern's medical staff will assess the ankle injury before informing Ottmar Hitzfeld of the 26-year-old's availability for the fixture with Bundesliga rivals Hertha.
"Owen needs to see our medical department and then we'll see what's going to happen," said Hitzfeld.
Meanwhile, Bayern are understood to have come to an agreement with Estudiantes for the signing of midfielder Jose Sosa.
Sosa is believed to be joining the German champions in the summer for a fee in the region of é¼7.8million (£5.25million).
"I have been thinking very carefully about what I was going to do because this will be a very big change, not only in my career, it's a big personal change too," Sosa said.
"I will have to get adapted in the best way possible and I hope to have many chances to play because that would make things easier for me."
Bayern have already captured Hamit Altintop and Jan Schlaudraff for next season, the pair agreeing to join from Schalke and Aachen respectively.
They could be joined at Bayern in the summer by Piotr Trochowski, who is being linked with a move back to his former club.
Trochowski has established himself as one of the Bundesliga's leading midfield players since leaving Bayern in 2004 for Hamburg and recently made his debut for the German national team.
The 24-year-old is tied to Hamburg until 2009, but according to Bild, a clause in his contract may allow him to leave earlier.