Manchester City defender Jason Denayer "regrets" becoming involved in a brawl outside a Brussels nightclub in which he "reacted instinctively" by kicking out at a man punching his friend.
An eight-second video of the incident - which took place on Sunday - shows the 21-year-old striking a man who is punching another man on the floor.
A longer version shows how Denayer, at first reluctant to intervene, strikes out when his friend is pinned down.
"I reacted instinctively," he said.
"Of course I regret to have been caught up in a conflict that was not mine to begin with, but I saw my friend was in real danger and I had to interfere and protect him."
Belgium international Denayer, who has been on loan with Sunderland this season, then left the scene in his car, which had been damaged by friends of the man he kicked, according to the player's agent.