The Congolese, from Belgian club Standard Liege, has already had a trial with Spurs, who are keen to sign him when he turns 16.
But now United have offered a trial to the highly-regarded youngster, who has a Belgian passport, and want to snap him up before he signs any formal deal with Liege.
Speaking of the situation, Mpoklu told the Daily Mirror: "I will have to wait a few months before I make a decision.
Mpoklu is the cousin of Porto defender Jose Bosingwa and gets advice from him.
"I have spoken a lot with my cousin and he gives me good advice," he said, adding: "I love English football, they have great players and the atmosphere in stadiums is amazing."