Rafiu transferred from Rivers United of the Nigeria Professional Football League to NK Maribor.
The 21-year-old helped Rivers United win the NPFL championship for the first time last season by scoring 14 goals.
Chijoke Akuneto, one of his teammates, won the top scorer prize with 19 goals.
In May’s friendly loss to Mexico, Rafiu made his international debut for Nigeria.
Maribor’s sporting director, Marko Uler, told the club’s official website, “We had to respond, to extend the personnel, and we also need a new answer in the wing positions.
I’m happy with the agreement we reached since Ishaq is now a player for the present and the future. He is well-recommended, including by the Nigerian champion.
“He scored 14 goals last season, which would have made him the greatest scorer in the championship if he had played in every game.
He is a player with physical power that is seldom seen, penetration, speed, and concreteness. It may indicate a wise decision for achieving our competitive goals as well as a move ahead for Maribor, since players from Nigeria frequently serve as a source of talent, he continued.