The Frenchman has got the new season off to a strong start, scoring two goals and creating two more to help United to the top of the early standings, but was hit with an injury blow last night as he limped off early during United's Champions League win over Basel.
"That's why you have such a strong squad," Rashford told reporters last night. "It's good for the manager, it's good for the players as well because we're always playing for competition.
"But Paul's going to be a massive miss and hopefully we can get him back fit as soon as possible. We have to play every game to win. If we want to be champions, then we have to win them types of games [against Everton].
"It's going to be difficult. Everton are a really strong team. They made some good signings in the summer and you know they've got strength all around the pitch so we have to come here and try and get the result."
Should Mourinho's assessment prove correct, Pogba will also miss league games against Southampton and Crystal Palace, as well as a Champions League game at CSKA Moscow.