Boateng has been instrumental at the back for the Germans, who have yet to concede a goal at the tournament.
He came off after 76 minutes and walked gingerly to the bench.
"I don't know exactly about Boateng. I hope the medical staff will succeed and I assume he will play in the next game," Loew said.
He said Boateng had felt his calf at halftime and that he had decided to take him off as a precautionary measure.
"The risk is too high and if something happens in the calf it means two or three weeks out for him so I didn't want to take that risk especially as Northern Ireland were not too dangerous in their attacks."
Germany finished top of Group C and will now face a third-placed team in the next round.
Image: Jerome Boateng
Photograph: Peter Cziborra/Action Images via Reuters
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