The 24-year-old joins Rostov after spending last season on loan at Nizhny Novgorod, where he scored five goals in 26 league appearances.
The former Golden Eaglets star made 100 appearances for Krasnodar, contributing 12 goals and eight assists.
Rostov confirmed his arrival on Friday through their official website.
“An agreement has been reached between our club and Krasnodar on the transfer of the Nigerian striker,” the club wrote.
“Olusegun began his professional career in the Danish Fremad Amager. In 2021, he moved to the Krasnodar club system.
“He made his debut for the main cast of bulls in the spring of 2022. He is the author of the fastest goal in the history of the Premier League: in October 2022, he scored against Rostov in the ninth second of the match.”
Olusegun earned his Super Eagles debut in a friendly against Russia in June 2025 and will now continue his career with Rostov.