Michail Antonio equalised in the 21st minuteWest Ham are investigating after German commentators were allegedly attacked by a Hammers fan during the 2-1 defeat by Eintracht Frankfurt.
The incident happened after West Ham's Michail Antonio equalised in the first leg of the Europa League semi-final.
West Ham said they "will be working to identify the offender".
The broadcasters, working for German station ARD, were commentating from the back row of the media section, which had supporters directly behind it.
"In line with our zero-tolerance approach, anyone identified will have their details passed to the police," said a West Ham spokesperson.
"They will be given an indefinite ban and be unable to enter London Stadium and travel with the club. There is no place for this kind of behaviour."
