Tottenham are investigating an allegation that one of their own supporters racially abused Son Heung-min during Sunday's defeat to Manchester United.
A Spurs fan tweeted that he felt compelled to confront another member of the home crowd after being disgusted by what he heard.
"I've not experienced racism at football for about 15 years," he wrote. "But today at @SpursOfficial was hideous. "Reported to stewards, confronted him myself and was called a c--t.
"While I was standing next to my son. Hideous."
A number of people were ejected from the home end on Sunday after Manchester United fans gained access.
The supporter later said the abuse came from a Spurs fan and was aimed at Son.
"Spurs have been in touch and I'll work with them to find the person," he wrote. "Stand-up to racism and it won't survive, let it go and it will just get worse.
"Spurs are looking into this now, and have been great."
When contacted by ESPN FC for comment the FA confirmed they are aware of the tweet and will be seeking more information from the relevant individuals and more details of the incident in order to determine the next step into investigating the allegation.
London police made three arrests for racially aggravated public order offences at the Carabao Cup semifinal first leg between Tottenham and Chelsea at Wembley last Tuesday.
Tottenham's clash with United was Son's last with the club for up to a month while he joins up with South Korea for their Asian Cup campaign.