The 21-year-old has made six league appearances since moving to Germany in the summer from Dutch side Roda JC.
Belgium Under-21 international Ngombo scored four goals in the Eredivisie for Roda.
He becomes the Dons' third signing of the transfer window, following Robbie Muirhead and Harvey Barnes.
Find all the latest football transfers on our dedicated page or visit our Premier League tracker here.
MK Dons have signed striker Maecky Ngombo on loan from German second-tier outfit Fortuna Dusseldorf until the end of the season.