Sunderland have confirmed Republic of Ireland international Darron Gibson will face an internal disciplinary process after he was filmed appearing to criticise team-mates after Saturday's 5-0 friendly loss to Celtic.

"Darron Gibson has not conducted himself in a manner befitting Sunderland AFC," a club statement said.

"We will initiate our internal disciplinary process."

The statement added: "Darron has apologised this (Monday) morning."

The video was filmed in a bar by supporters and posted on social media.