The centre-back started against Aston Villa last weekend as the side drew 0-0 and claimed a crucial point. He lasted just 45 minutes before being forced off at half-time and replace by Matthijs de Ligt.
Maguire was seen wearing a protective boot after the game and confirmed his injury setback on social media.
"Frustrated to pick up an injury at the weekend, will be a few weeks on the sideline for me but I'll come back stronger.”
United have a number of injuries to deal with already including Tyrell Malacia, Mason Mount, Leny Yoro, Alejandro Garnacho, Noussair Mazraoui, Kobbie Mainoo and Luke Shaw.
This is not ideal for a side who sit 14th in the league and are desperate to force their way back up the table and recover from one of the worst starts to a Premier League season in their history.
The injury may have come at a good time however as the international break could mean the 31-year-old is ready to face Brentford in their next fixture as long as he uses this two week break to rest and recuperate.