Ismaila Sarr is in London to undergo his medical at Crystal Palace.
The winger is set to sign an initial four-year contract with the Eagles after they agreed a deal with Marseille worth around £12.7million.
Sarr previously spent four years at Watford between 2019-23 after arriving from Rennes for a club-record fee of £27m, scoring 34 goals and registering 22 assists in 131 total appearances.
The 26-year-old returned to France last summer after joining Marseille, scoring five times in 35 outings for the French club as they finished an eventful campaign eighth in Ligue 1.
Sarr will now help fill the sizeable void at Palace left by the departure of star winger Michael Olise, who joined Bundesliga giants Bayern Munich for a fee of around £50m earlier in July.
The Eagles have been tracking Sarr for years and missed out on signing him in 2019 when he moved from Rennes to Watford.
Palace have made a strong start to the transfer window and are embarking on an aggressive recruitment drive this summer after sporting director Dougie Freedman snubbed interest from Newcastle to stay put.
Sarr is poised to become the third signing of the summer for the Eagles, who have already recruited Moroccan defender Chadi Riad from Barcelona following an impressive loan spell at Real Betis.
Palace also moved to reunite manager Oliver Glasner with former Eintracht Frankfurt midfielder Daichi Kamada on a two-year contract following his exit from Serie A outfit Lazio.
