Ulster wing Tommy Bowe has been ruled out of action for up to six weeks with a groin injury.
The Ireland wing sustained the injury while on international duty and after a scan today it was diagnosed as a muscle tear that could take between four and six weeks to heal.
It means the wing is definitely ruled out of this month's Heineken Cup double-header against Treviso, the first of which is at Ravenhil on Saturday (6pm), and is doubtful for the other Pool Five games against Montpellier and Leicester next month.
Prop Paddy McAllister is facing a similar spell on the sidelines after suffering a small tear to his hamstring..
However, captain Johann Muller has returned to training after injury and will be available this weekend. So, too, might Jared Payne (groin), who will be assessed later this week.
Outhalf Paddy Wallace (knee) will also be back after his long lay-off, having sustained a cruciate ligament injury in February and it is hoped scrumhalf Ian Porter will be available.
Backrow Mike McComish trained today after a blow to his hip in the win over Zebre, while Rob Herring will be reintroduced to full training this week after suffering a "stinger" against the Italian side.