Ulster have confirmed that Rory Best fractured his forearm during Ireland's last-gasp defeat to New Zealand on Sunday.
The hooker scored Ireland's second try at the Aviva Stadium but suffered the injury just three minutes later and will see a specialist in Belfast on Monday.
The loss of Best deepens Ulster's injury problems after three players picked up knocks during Friday's Pro12 win over Edinburgh.
Iain Henderson suffered a hamstring injury during the 41-17 victory at Ravenhill and will have an MRI scan on Monday to determine the extent of the injury.
Fellow forward Lewis Stevenson sustained medial ligament damage in his right knee and will be out for up to six weeks, while Michael Allen suffered concussion and will follow the normal return-to-play protocols.
Ulster were without Ian Porter and Nick Williams against Edinburgh after they suffered injuries ahead of the game with Edinburgh.
Porter irritated his AC joint and is expected to be unavailable for two weeks, while Williams' calf problem is expected to sideline him for up to six weeks.
Centres Darren Cave and Luke Marshall had cramp against Edinburgh but are expected to be available for Saturday's trip to Zebre.
Johann Muller and Jared Payne have been progressing well through their rehab and a decision on their involvement will be made later in the week.