Ulster Rugby skipper Johann Muller faces a race against time to be fit for the third and fourth rounds of the Heineken Cup after tearing a calf muscle.
The 33-year-old former Springbok lock is set to sit on the sidelines for up to six weeks after suffering the injury in last weekend's 39-21 PRO12 win over Cardiff Blues at Ravenhill. A scan on Monday revealed the extent of the damage.
Ulster won both their opening two Pool matches in the Heineken Cup, against Leicester Tigers and Montpellier, and Mark Anscombe is preparing his team for back-to-back clashes with fellow PRO12 team Benetton Treviso in rounds three and four in December.
Ulster are bidding for a fourth successive quarter-final qualification in the Heineken Cup and top their Pool by two points from the Tigers.