The slightly-built midfielder, who managed one goal in 18 league outings this season, was in and out of the first team as Leuven finished third in the Second Division standings in Belgium.
He missed the last two matches of the regular season through injury.
They are now to play in a four-team play-off for a single spot in the First Division next season. The clubs finishing second to fifth in the Belgian Second Division now compete in a mini league against each other, both home and away over the next weeks.
OH Leuven start on Saturday night away against KVSK United and then meet Tubeke and Antwerp, the club which is affiliated to English champions Manchester United has several of its younger players on loan.
The play-off matches will conclude on Tuesday, June 5 when Leuven are away at Tubeke.
The 23-year-old Mosia, who has been capped at Under-23 level by South Africa, went from the School of Excellence to Belgium in 2003, playing first at Westerlo and then Dessel Sport on loan.