The 25-year-old was purchased from Olympique Lyonnais for a massive €60m in 2019, but has struggled to make an impact in London, returning to Lyon on a six-month loan in January.
His contract runs to June 2025, so he can be sent out on loan, perhaps even with an option to buy.
According to Footmercato in France, Napoli and Villarreal are the clubs pushing hardest to get Ndombele this summer.
Other candidates included Milan, Real Betis, Aston Villa, Nottingham Forest, Everton, Bayer Leverkusen and Galatasaray, but none of those teams progressed beyond seeking general information.
Napoli need a midfielder to replace Fabian Ruiz, who is heading to Paris Saint-Germain for €20m plus bonuses, while Villarreal coach Unai Emery is known to be an admirer of the France international.