Arsenal midfielder Granit Xhaka was interviewed by police after allegedly racially abusing a worker at Heathrow airport, British media reported on Tuesday.
The incident happened on Monday, little more than 24 hours after Xhaka was sent off in a Premier League match against Burnley, a dismissal that will probably incur a four-game ban.
Xhaka had travelled to the airport to see off a friend flying to Germany, but reacted badly when his companion was refused entry after arriving late for the flight at Terminal Five, the reports said.
The Independent reported that a witness said the 24-year-old Switzerland international had racially abused a member of staff in German.
"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," a Metropolitan Police spokesman said.
"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."
Xhaka has now been sent off nine times in three seasons. If he is banned for four games he will miss Arsenal's FA Cup fourth-round clash with Southampton and league matches against Watford, Chelsea and Hull City.