Boxer Anthony Ogogo says he was racially abused by a fan after watching Norwich City in their Carabao Cup tie against Arsenal at Emirates Stadium.
The Canaries supporter, 28, believes he was targeted by a fellow Norwich fan who thought he was backing Arsenal in their 2-1 win on Tuesday.
Ogogo, from Lowestoft, said: "I was shocked. There's no place for that in football or anywhere for that matter.
"In this day and age it's disgusting. He said 'Go back to your own country'."
Middleweight Ogogo, who won bronze as an amateur at the 2012 London Olympics, played for Norwich City's youth team as a schoolboy before switching to boxing.
The London-based boxer watched Tuesday's game among home fans after his Arsenal-supporting friend let him use his ticket for the Carabao Cup fourth-round match.
"After the final whistle most of the Arsenal fans around me emptied out but I wanted to clap off the Norwich players because they'd given everything," he said.
"I went to the front of the stand and was clapping and singing in time with the Norwich fans below me. Then my friend said it looked as if an older guy with the Norwich supporters was trying to get my attention as if he knew me.
"I bent down to listen and quickly realised he didn't know me. He probably thought I was an Arsenal fan and he was shouting and swearing at me, saying pretty nasty stuff. I was flabbergasted.
"The player who scored our goal Josh Murphy is mixed-race and some of our great players have been black. This man must have cheered them on in his time.
"He was maybe in his seventies. I'm pretty thick-skinned as a professional athlete but it was really disappointing and a shame that it tarnished what should have been a nice memory for me because we played well even 'though we lost."
Ogogo does not intend to make a formal complaint about the incident and says he tweeted about it to raise awareness.
He said: "I'm not naive. I know things like this still happen but I've never experienced racism at Carrow Road my whole life and it won't stop me watching football anywhere.
"On the train home I was getting quite worked up by it. I don't want negativity or criticism for the club I love but I'm talking about it because this cannot be allowed to go on in 2017."
Norwich have asked Ogogo to supply further details of the incident in order that they can investigate it.
"We are very concerned by reports from Anthony Ogogo that he suffered racial abuse from a supporter in the Norwich section," said the club's statement.
"As a club we have a zero-tolerance policy on racism and all other forms of discrimination and we have contacted Anthony this morning.
"As always, any supporter found to be guilty of discriminatory abuse will be banned indefinitely by Norwich City and face possible criminal investigation."
Ogogo, who appeared as a contestant on Strictly Come Dancing, suffered a fractured eye socket in his last fight - a defeat by Craig Cunningham - and is preparing for a comeback.