Coach Joe Mazzulla said before Sunday's game against the Atlanta Hawks that Porzingis will be examined again "after a week or so."
Porzingis suffered the injury in a loss at Orlando on Friday afternoon. He has been enjoying a strong first season with the Celtics, averaging nearly 19 points on 54.7% shooting from the field.
Boston will also be without guard Jrue Holiday against Atlanta. Holiday has now missed two straight games with a sprained right ankle.
The Associated Press contributed to this report.