Mulumbu among six players to depart Kilmarnock after loan spells end
Youssuf Mulumbu is among six loan players to leave Kilmarnock after the club secured third place in the Scottish Premiership.
But midfielder Adam Frizzell, 21, has been handed a new one-year deal.
Mulumbu returns to Celtic after joining in January for a second spell at Rugby Park.
Daniel Bachmann, Aaron Tshibola, Conor McAleny, Mikael Ndjoli and Liam Millar also return to their parent clubs.
Ndjoli and Miller are out of contract this summer.
Kilmarnock are seeking a new manager following Steve Clarke's departure to take the Scotland job after guiding the club into the Europa League and achieving their record top-flight points total.
Frizzell spent the first half of the season on loan at Queen of the South but has endured an injury-hit campaign and underwent foot surgery this month.
"I've stalled this season through injuries but it's good to get another year and I want to recover and kick on," he said.