Lille want the same price Aston Villa paid Nice for the left-back last summer.
The report also suggests an Aston Villa player is essentially commanding the fee Lille are asking for the player.
The report suggests that Lille will not go lower than the €15 million (£11.6 million) that Aston Villa reportedly paid Nice for Jordan Amavi last season – as they feel the two are as good as each other.
This might just put Sidibe out of Watford’s price range.
The Frenchman has been superb for Lille this season and can play at both right and left-back positions.
The 23-year-old would however be an odd signing, considering the fact Watford officially announced Walter Mazzarri as their new head coach earlier today.
The Italian is known for playing three at the back and using wing-backs – which might not suit Sidibe’s style.
The former Napoli and Inter Milan boss was confirmed as the new manager of Watford this morning, taking over from Quique Sanchez Flores.