The 24-year-old Switzerland international was not arrested but visited a local police station after a different party reported the alleged incident.
Xhaka, who was sent off in Arsenal's 2-1 win over Burnley on Sunday afternoon, was interviewed under caution with Metropolitan Police confirming the details of the allegation in a statement released to PA Sport.
"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 statement read.
"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
When contacted by Press Association Sport, Arsenal said: "This is a private matter which is in the hands of the police."
Xhaka joined the Gunners from Borussia Monchengladbach last summer for a fee in excess of Â£30million.
He has recently enjoyed a run in the side but will serve a four-match ban having been shown his second red card of the season at the weekend.
Source : PA