Harry Maguire was arrested in the early hours of Friday morning after a fight between his friends and other Englishmen outside a bar in Mykonos, Greece.
After being knocked out of the Europa League in the semi-finals against Sevilla last week, the England international has headed to the Greek island to relax before the new Premier League season.
But Greek newspaper Proto Thema report that he was detained after an incident outside a bar on Thursday night. There has so far been no official comment from local police.
A statement from Manchester United read: “The club is aware of an alleged incident involving Harry Maguire in Mykonos last night.
“Contact has been made with Harry and he is fully co-operating with the Greek authorities. At this time we will be making no further comment.”