The centre-back, 32, joins Ruben Neves at the Saudi Pro League side following the Wolves midfielder’s £47m switch.
Chelsea midfielder N’Golo Kante has also agreed to sign for Saudi champions Al-Ittihad, while team-mate Edouard Mendy is close to joining Al-Ahli.
Koulibaly signed for Chelsea from Napoli last July on a four-year deal.
More to follow…