Cheikhou Kouyate will leave Crystal Palace on Friday after failing to agree a contract extension.
Kouyate, 32, was open to staying at Selhurst Park but wanted a two-year contract.
The defensive midfielder has been a Premier League regular since he joined West Ham in 2014 before making the switch to Palace in 2018 where he quickly established himself as an important member of the squad.
Kouyate has gone on to make 141 appearances for the Eagles, including 31 under Patrick Vieira last season.
Despite being a regular for Vieira's side, Kouyate will walk away from Selhurst Park on a free transfer as his contract expires.
Talks between the player and club over a new deal have been ongoing but have failed to find a positive resolution.
Given his age the Eagles were only prepared to offer the Senegal international a 12 month extension.
The former West Ham midfielder will now become a free agent on July 1 when his contract expires.
By completing a move for Lens midfielder Cheick Doucoure Palace have a younger, ready-made replacement.
The 22-year-old defensive midfielder made 34 appearances last season, chipping in with one goal and four assists as he formed an excellent midfield partnership with the in-demand Seko Fofana.
Doucoure was a key player in helping Lens to a seventh-placed finish in the club's second season back in the top flight, when they narrowly missed out on European qualification.
The Malian international has eight caps for his country and has spent his entire career at Lens, clocking up a total of 131 games.