The midfielder has two years left on his contract but has fallen out of favour at Spurs.
The 32-year-old is not part of Nuno Espirito Santo’s plans at Spurs and the PA news agency understands there is confidence a permanent deal can be struck before Tuesday’s transfer deadline.
Sissoko, who represented France at Euro 2016, has two years left on his contract at the Tottenham Hotspur Stadium but has fallen out of favour and is yet to feature this season.
He joined Spurs in 2016 as their club-record signing following a £30million move from Newcastle and has played 202 times, scoring five goals.
The box-to-box midfielder played an integral role in helping the club to the Champions League final in 2018/19 while he was also part of the team that challenged for the Carabao Cup and Premier League
He would provide good experience to the Hornets team as they return to the top tier following promotion from the Championship last term.
His possible departure marks another step in Tottenham’s rebuild as he looks set to follow Danny Rose, Erik Lamela and Toby Alderweireld out of the door at Spurs.
The clubs meet on Sunday in the Premier League as Watford visit north London.