Rashford made his first United appearance since December 2024 on Saturday, coming off the bench in the 4-2 pre-season defeat by AC Milan. The 28-year-old spent the second half of last season on loan at Aston Villa before moving to Barcelona, but the LaLiga champions decided against signing him permanently.
His return to United has therefore been a major talking point during pre-season, although Carrick has yet to confirm whether Rashford will remain beyond the September 1 transfer deadline.
Maguire, however, believes United would benefit from keeping the England international.
"Obviously the transfer window is still open," Maguire said. "As players, we hope he stays because if he does, he is a big asset to have. He can improve us for sure.
"You saw when he came on, he threatened the backline really well. He could have scored. He's a huge threat."
Rashford was handed the No.9 shirt against Milan and showed glimpses of his attacking ability during his 30-minute appearance. United have stressed that the number is not necessarily permanent, with Benjamin Sesko, who had been expected to take the shirt, unavailable because of injury.
The forward's involvement nevertheless suggested he remains part of Carrick's thinking, although United have not completely closed the door on a transfer.
Maguire, who has played alongside Rashford for several years, also believes having the striker back in training can benefit the rest of the squad.
"I've played with Marcus for numerous years and I know that playing against him and playing with him in training is going to help us," he added.
Carrick was again non-committal about Rashford's future after the Milan defeat.
"A lot of the boys will be better for the minutes," he said. "We've got a good squad, so there are decisions to be made."
For now, Rashford appears increasingly likely to remain at Old Trafford, with his teammates clearly eager to see him given the opportunity to rediscover his best form. However, until the transfer window closes, his United future remains unresolved.
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