Watford are in talks with Rennes about a club-record-breaking deal to sign winger Ismaila Sarr, according to Sky Sports.
Any deal for the 21-year-old Senegal international Sarr would break Watford's transfer record fee of £18m - which they paid to Burnley for forward Andre Gray.
Italian side Roma are also reported to have held talks with Sarr, and one source claims Arsenal are interested in signing him if they cannot complete a deal for Crystal Palace winger Wilfried Zaha.
Watford are also understood to be speaking to Lille about selling striker Dodi Lukebakio, but both clubs are in disagreement about the valuation of the player, with the Premier League side wanting around £13m for him.
Lukebakio, who has only made one Premier League appearance for Watford, spent last season on loan at Fortuna Dusseldorf, where he scored 10 league goals in 22 starts for the German club.
Watford also still retain an interest in Nice winger Allan Saint-Maximin for a club-record £25m, according to Sky sources.
The 22-year-old scored six goals in 29 games in all competitions for the French side last season, as well as providing three assists.
However, his future remains unclear after appearing to have fallen out of favour with former Arsenal midfielder and current Nice boss Patrick Vieira.