Ulster and Ireland wing Tommy Bowe has been ruled out for up to six weeks after suffering a groin injury while on international duty.
A scan on Tuesday revealed that the 29-year-old has suffered a muscle tear, meaning he will miss Ulster's Heineken Cup double-header against Treviso and the RaboDirect Pro12 games against Zebre and Irish rivals Leinster and Munster.
Ulster captain Johann Muller is expected to face Treviso in Saturday's Pool 5 clash at Ravenhill, as is Paddy Wallace, who has returned to full training following the anterior cruciate ligament injury he suffered in February.
Jared Payne continues his recovery from a groin injury and will be assessed later in the week, while back-rower Mike McComish, who sustained a blow to his hip joint against Zebre last weekend, was able to train on Tuesday.
Prop Paddy McAllister has been ruled out for between four and six week after re-aggravating a hamstring injury, while hooker Rory Best will be out until the New Year with a fractured arm.