The former Celtic defender has had a difficult start on Wearside.
The 23-year old arrived from Celtic in July but has made just two appearances after suffering an ankle injury in the Black Cats' 6-3 League Cup triumph over Exeter at the end of August.
Matthews was due to feature in a training ground friendly against Sheffield United today - according to the Sunderland Echo - as he eyes a return to first-team football.
Billy Jones assumed the right-back berth in the Welshman’s absence and deadline day loan signing DeAndre Yedlin has further increased competition.
The former Celtic man will now need to impress a new manager following Dick Advocaat’s departure, as his disrupted return to English football continues.
Matthews was a regular at Celtic before the arrival of Mikael Lustig and has proven himself at the highest level in European competitions.
Whether or not he can return to his best form in the Premier League is another matter entirely, but the Black Cats’ woeful defensive record this season suggests there’s every chance he gets a shot.