The former Lobi Stars talisman scored 13 goals in 23 league appearances to help the Monastir-based outfit finish third in the 2019-20 Tunisian top-flight table.
Okpotu was not in action on Sunday as US Monastir ended their league campaign with a 1-1 draw against Ben Guerdane at home. They join fourth-place Etoile du Sahel as Tunisia's representatives for next season's Caf Confederation Cup.
Following his landmark feat, he will shift his attention to Wednesday's Tunisian Cup game when US Monastir visit Ligue 2 outfit EGS Gafsa for a place in the semi-final.
Okpotu moved to Tunisia last August after spending a year with Moroccan side Difaa El Jadida. He struggled for playing minutes in El Jadida and he was sent out on loan to Albania to join Laci for the remainder of the 2018-19 season.
During his debut campaign in Tunisia, the Nigeria international scored two braces this year - against Stade Tunisien and Hammam-Lif.
Okpotu was part of the Super Eagles' team that made it to the final of the 2018 African Nations Championship in Morocco where they lost to the hosts 4-0.
He played in all of Nigeria's games at the tournament with two goals to his name.