The youngster celebrates his 17th birthday today, meaning that he is now free to agree a pro deal with Birmingham or any other interested parties.
Bellingham has been a regular member of the first team this season, making 37 appearances for the club - including 34 in the Championship - at the age of just 16.
The Englishman's performances have led to interest from United and Dortmund, both of whom are hopeful of snapping the prospect up this summer.
Recent reports suggest that Dortmund have won the race for his signature, with Bellingham noting Jadon Sancho's progress at the German outfit during his decision to pick them over a move to Old Trafford.
The deal is thought to be worth an initial £15m, although that could rise to close to £25m with add-ons and bonuses.
Bellingham has scored four goals and created three more in his 34 Championship appearances to date. body check tags ::