United say they are investigating the matter as a priority, and PA Media reports that police have been informed.
It is understood the situation could lead to an indefinite ban.
A United spokesman said: “We are aware of an incident at yesterday’s game where an individual in the home section has allegedly engaged in racial abuse.
“The individual was identified and ejected from the stadium. We are currently investigating the matter as a priority.
“Racism and all forms of discrimination are completely unacceptable and do not reflect the values of our club.”
The news comes on the same day that two men were arrested following reports of racist abuse during an FA Cup match between Haringey Borough FC and Yeovil Town on Saturday.
The men – aged 23 and 26 – were arrested in Chard and Yeovil on suspicion of racially aggravated common assault, the Metropolitan Police said. Both are in custody at a Somerset police station.
The match – which was held at Haringey’s Coles Park ground – saw both teams led off the pitch by their managers in the 64th minute following the alleged abuse.
Haringey manager Tom Loizou said that defender Coby Rowe had suffered racist abuse and goalkeeper Douglas Pajetat was also said to have been spat at and had missiles thrown at him.
The FA said it is “deeply concerned” about the allegation and is looking into the incident “as a matter of urgency”.