Xhaka is believed to have been seeing off a friend who had visited him in London. The man is understood to have arrived late for his flight back to Germany and was not allowed to proceed to board.
It is at this point that the racial abuse is alleged to have occurred.
A spokesmen for the Met told BBC: "Police were called at 19:29hrs on Monday, 23 January following an allegation that a member of staff had been racially abused at Heathrow Airport, Terminal Five.
"The allegation was made by a third party.
"Officers attended and spoke with a man in his 20s. He was not arrested. He voluntarily attended a west London police station where he was interviewed under caution. Enquires continue."
Arsenal have declined to comment other than to say it is a private matter that is now in the hands of the police.
The incident occurred just over 24 hours after Xhaka was sent off during his team's Premier League game against Burnley.