The 22-year-old forward has signed a three-year contract with the Whites and will be available for selection on Saturday when the Sky Bet Championship season kicks off at Millwall.
The former Manchester United youngster has over 100 Football League appearances to his name and has scored over 30 goals.
During his time at Peterborough the young striker enjoyed loan spells at Scunthorpe, Chesterfield, Crawley, Bury and most recently at Swindon.
On his return to ‘The Posh’ from Swindon the forward netted five goals during January of this year and won the League One Player of the Month award.
Nicky also has international caps on his CV from when he played for England’s Under-16s and Under-17s.The striker is also eligible for Nigeria.
United head coach David Hockaday said: “Nicky was involved with a very good group of players in the Manchester United Academy and he was one of the high flyers in that group.
“He can play up front in a number roles and he is very talented. He is a super professional and is an ideal addition to our squad.”
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