Still only 18, the defender impressed during the recent win over Zorya in the Europa League, his driving run from right back a key component in Zlatan Ibrahimovic’s only goal.
United believe Fosu-Mensah has the build and technical ability to thrive at Old Trafford, while talks have been ongoing since the summer.
He penned a first professional contract in August 2015 and is set to lengthen that stay once fresh terms have been thrashed out.
Sportsmail understands only minor details are left to complete before Fosu-Mensah commits to the club for a further four or five years.
Jose Mourinho is known to be an admirer of the Holland Under 21 international and tying the former Ajax trainee down is seen as a coup around Carrington.
He was always going to survive the cull of younger players at United once Mourinho arrived, with academy bosses glowing about his development before Louis van Gaal handed the player 10 appearances towards the end of last season.
“It’s going well,’ Fosu-Mensah said recently. “I have not played much, but train with the first-team and do everything with the first-team. I want to fight myself in there.
“I talk to Jose Mourinho about my development, which is going well. Mourinho has faith in me, so he keeps me in the selection.”