The centre-back only played 45 minutes on Tuesday as Germany booked their place in the final with a stunning 7-1 victory over hosts Brazil, with the Dortmund man confirming after the match that the problem had been bothering him for a few days.
Coach Joachim Low opted to withdraw him at the break with Germany 5-0 ahead and cruising into Sunday's final.
However, team manager Oliver Bierhoff still expects the defender to be involved and insisted Low had only substituted the 25-year-old as a precaution.
"Everyone's okay except for Mats Hummels and he's getting further treatment," Bierhoff told German TV station ARD.
"It's a precautionary measure. We assume he'll be able to play in the final."
Hummels revealed he had been nursing the problem prior to the semi-final.
"I've had problems with it for a few days," he said. "But for the first time it didn't go away after warm-ups. In the match it got worse and worse.
"I made the decision that it's perhaps better to take myself out so that I wouldn't break anything.
"We'll have to see exactly what it is. It's not something tiny but fortunately I don't think it's anything that would endanger Sunday."
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