The 22-year-old is rejoining Lee Bowyer's Blues squad as they look to pull away from the relegation zone in the Championship.
Chong had started life at St Andrew's well until suffering a ruptured thigh tendon that required surgery in early November.
The Academy graduate did rehabilitation work at Carrington and is now able to return to the Midlands in order to regain full fitness.
Birmingham lost 3-1 at promotion-chasing Bournemouth on Wednesday night and another United loanee, Teden Mengi, was forced off the field at the Vitality Stadium with an injury.
“Young Teds is a 19-year-old kid and he has just felt his hamstring there as well," commented Bowyer afterwards.