Trevor Carson will miss an extended part of the season after developing deep vein thrombosis.
DVT is a blood clot that develops within a deep vein in the body, usually in the leg, groin or arm.
The Northern Ireland international took ill on Wednesday and received specialist care from the staff at University Hospital Wishaw.
The 30-year-old is now on the mend, but will require ongoing treatment that will rule him out for an as yet unspecified amount of time.
“We would like to thank all the staff at University Hospital Wishaw for their diligence and care, given it is the sort of medical emergency that can be and often is life threatening if not treated promptly and correctly,” manager Stephen Robinson said.
“It’s not your usual injury in that at this stage, his return time is not yet fully known and will obviously depend on a number of factors.
“As a club, we wish Trevor a very speedy recovery and will give him all the support he needs to get back fit and healthy as soon as possible.”