Sunderland sign Celtic's Adam Matthews

Celtic defender Adam Matthews has completed his move to Premier League side Sunderland for a fee of £2m.

The 23-year-old full-back has signed a four-year contract at the Stadium of Light.

"We know that we need quality players to improve competition for places in the side, so Adam is a welcome addition to our squad and we are very pleased to welcome him to Sunderland," Black Cats head coach Dick Advocaat told the club's official website.

Matthews, who has 12 caps for Wales, joined Celtic from Cardiff City in 2011. He made over 100 appearances for the Hoops, and won four Scottish Premier League titles.