The Dutch born Ghanaian teenage defender
United manager Jose Mourinho was keen to seal the 18-year-old Dutchman's future at Old Trafford to underline his commitment to the club's tradition of developing young players.
Fosu-Mensah impressed in his 10 first-team appearances for United last season under Louis van Gaal, making his debut as a substitute for Marcos Rojo in a 3-2 victory against Arsenal in February.
An announcement could be made as early as Friday as Fosu-Mensah, who is expected to serve as an understudy to Antonio Valencia at right back this season - prepares to follow fellow academy graduates Marcus Rashford and Cameron Borthwick-Jackson by penning a new contract.