Egyptian judoka Islam El Shehaby received boos and whistles from Olympic spectators Friday when he refused to shake hands with his Israeli opponent Or Sasson.
After losing to Sasson in the first round in the 100-kilogram competition, Shehaby was so disappointed that he did not stand up from the mat at first. When Sasson then stretched out his hand to the Egyptian, Shehaby refused to take it and turned away, shaking his head.
Shehaby did not want to comment on his behaviour afterwards.
Israel is seen as an enemy nation in many Arab countries.
International Olympic Committee spokesman Mark Adams said he did not want to comment before having established the facts of the incident.
"We'll obviously look into it," he said.
"I mean, what I would also say is things happen in the heat of the moment that are not acceptable," he added. "We believe that the Olympic movement should be about building bridges, not erecting walls."
The incident did not go over well in Israel, where Prime Minister Benjamin Netanjahu's spokesman Ofir Gendelman described it as "shocking" in a tweet.
"Egyptian Judoka Islam Shihabi refuses to shake hands w/ Israeli Or Sasson, goes against spirit of #Rio2016," read the tweet.