Son of United legend, Darren, he joined the Academy from Manchester City last year along with twin brother, Tyler. He then signed his professional contract in April, shortly after his 17th birthday.
Fletcher arrived at Old Trafford as part of the first-team squad early on Saturday afternoon and will take his place among the substitutes at M16.
Fletcher has made a fine start to the season at Premier League 2 level, getting a goal and two assists in successive United wins over Stoke City and Blackburn Rovers in August.
Those performances earned Jack a nomination for Premier League 2 Player of the Month, while he also scored twice off the bench in our EFL Trophy victory against Barnsley in September.