RaboDirect Pro12 leaders Ulster will be without Lewis Stevenson for up to six weeks due to a knee injury.
The in-form second row sustained the knock in Friday's 45-20 victory over Edinburgh at Ravenhill.
The 28-year-old limped from the field of play after suffering medial ligament damage and will be out for at least a month.
Ulster are hopeful the former Harlequins man could return in time for their Heineken Cup double header against Northampton next month.
Neil McComb is the club's only fit lock with captain Johann Muller sidelined with a thumb injury while Dan Tuohy and Iain Henderson are training with Ireland.