Amad Diallo has completed his move to Manchester United from Atalanta, signing a contract until June 2025.
His transfer, announced on October 5, was subject to a medical, work permit and personal terms which have all now been finalised.
The 18-year-old has featured twice for Atalanta this season: once in Serie A and in the Europa League.
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Ole Gunnar Solskjaer said: "As a club, we have followed Amad for a number of years and having watched him myself, I believe he is one of the most exciting young prospects in the game.
"Manchester United has such a proud history of developing young players and everything is in place to enable Amad to reach his potential here.
"It will take time for him to adapt but his speed, vision and fantastic dribbling ability will stand him in good stead to make the transition.
He is a player with all of the raw attributes that are needed to be an important player for Manchester United in the years to come.
Once his work visa has been issued, Diallo will be cleared to travel to Manchester and to train with and play for United.
He told the club website: "After waiting since the summer, it is finally a dream come true to complete my move to Manchester United. I am hugely ambitious and there is so much that I want to achieve in the game; when I spoke to the manager I knew that I had joined the perfect club.
"his is a really exciting squad with so many great players, I can promise that I will work hard every day to learn from them and give everything to develop my game.
"The coaches have been fantastic since I signed, we have been in touch regularly and they have already given me a lot of great advice. I have had time to prepare for this move, both physically and mentally, and I have worked really hard to be ready to make the step up to this amazing club."
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