The 30-year-old’s previous deal expired last month leading to links with a move to former club Hibs, or following Scott Brown to Aberdeen – but all that ended when Ange Postecoglou made a one-year extension one of his first acts as Celtic manager.
However Griffiths has yet to feature for the new Hoops boss in their preparatory games ahead of the new season and Sunderland are now being linked with a loan move for the forward to spearhead their promotion bid from skybet League One, according to The Sun.
The Black Cats defeated Hearts 2-0 on Saturday while Griffiths was again missing from Celtic’s squad in their 1-0 loss to Preston North End.
Griffiths’ absence from Postecoglou’s four friendlies against Sheffield Wednesday, Charlton Athletic, Bristol City and Saturday’s disappointing home defeat, comes after the striker was sent home from Celtic’s pre-season camp in Wales pending club and police investigations into online messages allegedly sent from his social media account. Police later said no criminality had been established after their assessment of the situation.
A potential switch to Wearside could see the 30-year-old replace Charlie Wyke at the Stadium of Light after the striker moved to Wigan Athletic, despite heavy and frequent links with a move to Celtic of his own.
Scotland international Griffiths has been with Celtic since January 2014, scoring 123 goals in all competitions but found first-team appearances hard to come by last term – starting just nine times.