The 16-year-old midfielder made his debut for the Red Devils in their 3-2 defeat to Wolves on Saturday in the Under-18 Premier League Cup.
The France Under-17 international caught the eye of the United coaches during a spell at their pre-season training camp in Austria.
"Traore is a boy we've been looking at for a while," U18's coach Kieran McKenna, told MUTV.
"He is a really powerful midfielder who likes to run box to box. He is very strong technically and is improving all the time."
"He's a nice man and his English is improving. He's settling in well with the boys and has taken to the club really well."
Traore turns 17 in January and will be available for United's FA Youth Cup campaign which starts on December 13 against Derby.
ICYMI - #MUFC have completed the signing of French youngster Aliou Traore: https://t.co/MFS8ZoFUU7 pic.twitter.com/rzw8rZ0wIx
— Manchester United (@ManUtd) 3 December 2017