United announced during the summer that they had completed a deal for the young winger, but needed to iron out details regarding a work permit and personal terms before bringing him to Old Trafford.
These issues have now been resolved and Diallo will be free to play for the club as soon as his request for a visa is granted.
He has impressed during his time in Italy and has been tipped to achieve great things with the 20-time Premier League champions.
Gomez, Diallo’s former team-mate, has revealed that his Atalanta colleagues struggled to deal with his pace and trickery during training.
He also likened the talented winger’s style of play to that of six-time Ballon D’Or winner Messi.
“There are defenders in the first team that sometimes cannot stop him,” Gomez told United’s official website. “To stop him in training, we have to kick him! He plays like Messi.”
Diallo has played 46 times for Atalanta in total, but has only made two appearances this season.
He was introduced from the bench during November’s league defeat at the hands of Hellas Verona, before another late cameo in the Champions League draw with Midtjylland three days later.
The 18-year-old found the net on his senior debut for Atalanta last season, becoming the first player born in 2002 to score in Italy’s top flight.
United boss Solskjaer praised his side’s latest acquisition upon the announcement of his arrival, claiming that Diallo is already among the best young players in the world.
“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,” Solskjaer told the club website.
“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.”