Alongside Kouyate, forward Emmanuel Dennis is set to have a medical, and Swiss midfielder Remo Freuler passed his last night.
The 32-year-old is set to join his third Premier League side, and brings a wealth of experience to a squad made up of many players entering their first top flight season in England.
Described as a ‘top player’ by former teammate Scott Dann, Crystal Palace decided against renewing Kouyate’s contract but could be reunited with their former player when the two sides meet in November.

Forest set to sign Kouyate on free transfer
Kouyate could end up being a brilliant signing for Forest given his versatility.
A capable ball player and strong tackler, Kouyate has been deployed as both a centre-back and holding midfielder at Palace and West Ham.
Steve Cooper tends to set his side up with three centre-backs and two midfielders sitting in front of them, and Kouyate could fill any of these roles.

Moussa Niakhate has already been recruited to compete at the back, while Orel Mangala and Lewis O’Brien have both improved Cooper’s midfield options.
If all three players are confirmed by Forest, that will take their number of signings to 15 for the summer, but they might not be done yet.
Steve Cooper’s side have been linked with another winger, and could even make an audacious move for Tottenham’s Tanguy Ndombele.
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