The youth team star, who did play first team football last term, has signed for Villarreal.
Kambwala is heading to the Yellow Submarines in a £9.6m deal, having arrived at United from Sochaux in 2020.
He wrote: “Dear Manchester United, I arrived at the club as a boy with a dream and today I’m leaving like a young man who has fulfilled his dream,” he wrote.
“From the academy to the first team, it’s time for me to start a new adventure after wonderful seasons at the club.
“Thank you to all the people I have met during these years. Coaches, my teammates, staff members, workers in Carrington and members of my host family. I’ll never forget what you all did for me.
“A special thank you to you fans who have always supported me, you are the soul of this club. I wish you the best for this season and for the future.”