Yokohama Marinos President Akira Kaetsu apologised profusely after one of the club's fans waved a banana at Kawasaki Frontale's Brazilian striker Renato on Saturday, describing the act as 'unforgivable'.
Marinos banned the supporter indefinitely after the teenager was identified by club officials when the footage went viral.
"I'd like to apologise to the members and staff of Kawasaki Frontale and their families. I'm very sorry about this incident," Kaetsu told reporters in Tokyo on Monday. "It's unforgivable. We will not tolerate any acts of discrimination.
"The fan is denying that he had any racist intentions, but we explained that while you may not think so, people perceive it differently."
The incident comes five months after fellow J.League outfit Urawa Reds were forced to play a home game at an empty stadium as punishment for their fans unveiling a banner deemed discriminatory.
J.League chairman Mitsuru Murai promised swift action.