According to Sky Sports, the Black Cats have taken a giant step towards completing a deal for Wales international Matthews.
The 23-year old right-back has recently been linked with a return to former club Cardiff City but it appears as though he is on his way to England with Dick Advocaat poised to lure him to the Stadium of Light.
Matthews joined Celtic from Cardiff in 2011 and has helped the Glasgow giants win four Scottish league titles since his arrival at Parkhead.
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