The Germany captain hobbled off just before halftime in Wednesday night's friendly and it was unclear if he would be fit for Saturday's Premier League match at home to Middlesbrough.
A Chelsea spokesman said on Thursday it was too early to say how bad the midfielder's injury was.
"The injury is obviously daft for me because I've come through the season so far without any injury," Ballack told German television.
"But I'll have to wait and see how serious it is."