Michael Ballack suffered a thigh injury in Germany's 3-1 victory over Switzerland in Dusseldorf on Wednesday.
Ballack played a key role in Germany's opening goal
The Chelsea midfielder limped off the pitch one minute before the break after straining his right thigh and did not return for the second half.
"It is definitely a strain, but I hope it's not serious," said Ballack.
"We have to wait and see in the next few days how the pain is. It's annoying as I've been getting through the season quite well in terms of injuries."
Chelsea play Middlesbrough at Stamford Bridge on Saturday.
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