The defender has been sent back to Old Trafford from international duty in order to receive treatment on the ailment.
Cathcart, who spent last season on loan at Plymouth, suffered the setback while turning out for Northern Ireland U21s.
He was unable to prevent his country from slipping to a 2-0 European Championship qualifying defeat against Czech Republic and has now been laid low with injury.
The problem wraps up a disappointing week for the 20-year-old, who saw a move to Newcastle break down at the last minute prior to Tuesday's transfer deadline.
Cathcart will now sit out Northern Ireland's next qualifier against Iceland on Tuesday, as will Blackburn defender Johnny Flynn, who has a knee problem.