Ex-Wales and Celtic striker John Hartson has suggested that Adam Matthews is taking a big risk by joining Sunderland.

The 23-year-old full-back made a move to the Black Cats in a £2m deal from the Scottish Premiership champions earlier this week.

Matthews appeared 42 times for Celtic in all competitions last season, but Hartson believes that his former side's decision to snap up Saidy Janko may have played a big part in his compatriot's decision.

"It's a brave decision, but I'm sure it's all about getting regular football," he told BBC Sport. "I think if he's not promised that at Celtic and he's guaranteed to play more at Sunderland, then I can understand."

Matthews joined Celtic from Cardiff City in 2011, featuring 148 times for the Glasgow club during that time.