The Gabon international could be on his way out of the Stadium of the Light outfit after they dropped to the English third tier Didier Ndong has been linked with newly promoted English Premier League side Cardiff City from Sunderland.
The 23-year-old joined the Black Cats in August 2016 from French Ligue 1 side Lorient after signing a five-year contract and featured 54 times, scoring once since his arrival.
However, in January, he was acquired by Watford on loan with an option to make the deal permanent but having failed to make a single appearance for the Hornets, they refused to trigger the clause which could have helped him continue his stay at the Vicarage Road outfit.
The midfielder is believed to fancy a chance to return to the top-flight and interests have been shown by some French sides.
However, Cardiff, according to Watford Observer, is believed to be in pole position to sign him.
Sunderland were relegated last season from the English Championship to League One and will be aiming to scoop the £13.6 million [excluding add-ons] paid for the services of the midfielder in 2016.