The youngster was able to sign professional terms as soon as he turned 17 years old.
Obi-Martin, who signed on an initial scholarship deal from Arsenal in the summer, is already scoring for fun at youth level.
Per Manchester Evening News, United's coaches will be challenged with holding back Obi-Martin.
The forward wants to play more often and he does want to get first-team chances as soon as possible.
One of the reasons he left Arsenal was that he felt his pathway to the first team was not clear.
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