Rashford has not played for United since he fell out of favour with former manager Ruben Amorim in December 2024, spending the last 18 months out on loan with Aston Villa and Barcelona.
The 28-year-old's future at his boyhood club remains unclear, though United's new manager Michael Carrick last week described the England international as "our player".
Rashford, who returned to United's squad last week following an extended break after the World Cup, came off the bench in a 4-2 pre-season defeat by Italian club AC Milan on Sunday.
"Obviously the transfer window is still open. As players, we hope he stays because if he does, he is a big asset to have. He can improve us for sure," defender Maguire said after the loss.
"You saw when he came on, he threatened the backline really well. He could have scored. He's a huge threat.
"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."
United, who finished third last season, begin their Premier League campaign with a trip to promoted Hull City on August 22.