The Belgium midfielder, back from a calf injury, was brought off the bench just 19 minutes into the Group A opener after Pogba's night was abruptly halted during an innocuous passage of play.

Having led United out as captain for the first time, a night that started as one to remember swiftly unravelled as the 24-year-old pulled up holding his hamstring after going into a challenge.

Mourinho's initial prognosis was to expect Pogba will be out for a "few weeks", although further assessment is required on a player who left Old Trafford on crutches.

Sunday's return to Premier League action at home to Everton certainly looks out of the question and Rashford says United will understandably miss one of the stars of the early weeks of the season.

"That's why you have such a strong squad," the 19-year-old forward said.

"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 (like Sunday's).

"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."

Rashford is confident of this weekend building on Tuesday's "solid" start to Group A life against Basle - a night when the 3-0 scoreline fairly reflected United's dominance.

For the 19-year-old, it was a first taste of Champions League football and, like so many times before, a competition debut he capped with a goal.

Rashford has looked bright in the early weeks of the campaign but, much like Anthony Martial, has been unable to nail down a starting berth due to impressive attacking options the teenager believes are helping rather than hindering his development.

"It's difficult when you're in and out of the team, but we have to find the positives out of it and I think we have both done that," the England international said.

"I think the competition is always positive competition because we're improving each other every day when we're in training and in the games we're pushing each other more and more.

"It's a bit of a headache for the manager but it is a good headache to have."

The summer arrivals of Victor Lindelof, Nemanja Matic and Lukaku have increased competition across the park, while those returning from injury will swell the group further.

Luke Shaw has played several times for the Under-23s on his way back from ligament damage in his foot, while Marcos Rojo has begun training with the first-team as he recovers from knee ligament damage.

Zlatan Ibrahimovic hopes to be back before the end of the year and Ashley Young showed no sign of rust on his first-team return on Tuesday, putting in a fine display at right-back as well as an exceptional cross for Fellaini's opener.

"That's the quality that he possesses," Rashford added on Young.

"He's been there, he's done it, he knows what games require so we didn't expect anything less from him.

"We're happy because he hasn't played for a while and he's been able to come straight back into the team and perform."