Tottenham are investigating allegations that Son Heung-min was racially abused during Spurs' defeat to Manchester United at Wembley on Sunday.
Spurs supporter and journalist James Dickens claims the abuse was directed at Son by a spectator. He says that, when he confronted the fan, he was sworn at.
A statement from a club spokesman read: "We are investigating an incident involving alleged racial abuse directed towards Heung-Min Son in Sunday's game against Manchester United.
"Whilst the incident occurred in the home end, we are yet to determine if the alleged individual was a Tottenham Hotspur supporter or not.
"Any kind of racist, discriminatory or anti-social behaviour will not be tolerated by the Club.
"We have a strict, zero tolerance attitude in this regard and shall take action against anyone behaving or using language that is abusive, offensive or obscene."
Dickens confirmed he is working with the club to identify the culprit, tweeting: "I've not experienced racism at football for about 15 years. But today at @SpursOfficial was hideous. Reported to stewards, confronted him myself.
"Spurs are looking into this now, and have been great."
Tottenham found themselves in hot water last month after a fan threw a banana skin at Arsenal striker Pierre-Emerick Aubameyang, who is of mixed race.
The fan in question was fined and handed a four-year football banning order.