Rashford, who signed a five-year deal at Old Trafford this past summer, has struggled for form this season, scoring two goals in 18 games in all competitions, with his latest performance in a 1-0 defeat to Newcastle United bringing fresh criticism.
In Rashford's place, United manager Erik ten Hag selected Brazilian winger Antony in a forward line alongside Rasmus Højlund and Alejandro Garnacho. Anthony Martial also drops to the bench from the loss to Newcastle.
Rashford eventually entered the game as a replacement for Højlund in the 84th minute. Man United won the game 2-1, thanks to two goals from Scott McTominay.
Ten Hag had backed Rashford to rediscover his form after the Newcastle loss, saying: "He works hard and he's investing a lot. He will get back, he will recover and he gets all our support."
Ten Hag is battling to keep key players onside, sources have told ESPN, with some first-team players becoming disillusioned after a 10th defeat of the season at St. James' Park.
A number of players remain behind Ten Hag and his staff, but there are concerns within the club that the mood inside the dressing room will dip even further unless there is an upturn in form soon.