Jason Denayer was filmed kicking a man in the head during a brawl outside a bar in Brussels.
The 21-year-old, who spent the season on loan at relegated Sunderland from Manchester City, headed back home to Belgium at the weekend.
A video emerged of Denayer landing one blow on a man restrained on the floor before others stepped in.
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Denayer admitted his regret after the incident but claimed he was defending a friend.
‘I was on my way to my car when I heard a friend shouting,’ he told the Belgian press.