The injury only came to light when the South African saw a specialist yesterday and he is expected to be out of action until January.
Coughlan was omitted from the original squad after suffering a torn groin in the September RaboDirect PRO12 in Ravenhill. At that time the prognosis was for a five month recovery period.
However, Coughlan who was particularly diligent about his rehab has returned to action way ahead of schedule to be registered ahead of the midday deadline.
Ivan Dineen who was registered in place of Coughlan back in September, is now de-registered as per competition rules.