The Scotland international received his fifth yellow card of the domestic season during the Reds' pulsating 2-1 win over Everton at Goodison Park.
McTominay had only just come on as an 83rd-minute substitute for Christian Eriksen when referee David Coote booked him for a challenge on Demerai Gray.
However, the combative midfielder still played an important role in helping United repel some late attacks from the hosts to see out a precious victory.
McTominay was previously cautioned in the 3-1 win over Arsenal and 1-0 victory at Southampton, as well as the two early-season defeats to Brighton & Hove Albion and Brentford.