An assessment this morning has confirmed that Ulster star Nick Williams sustained medial ligament damage to his left knee in the Heineken Cup Pool 4 win over Glasgow at Ravenhill last Friday.
The number 8 and is expected to be out for up to eight weeks.
Prop Adam Macklin also damaged his knee playing for the Ravens against Bristol at the weekend.
He will be subject to an ongoing conservative management programme and will be reviewed in due course.
Outhalf Paddy Jackson was assessed yesterday for an ankle injury he picked up against Glasgow, as was winger Craig Gilroy who suffered a bang to the head on Friday night.
Jackson’s ankle is responding well to physiotherapy treatment, while Gilroy is following the necessary return-to-play protocol.
It is hoped that both players will be available for selection for this weekend’s Heineken Cup game against Castres Olympique.