Leinster Rugby back-row forward Sean O’Brien looks set to miss the rest of this season’s Heineken Champions Cup Pool stage with a broken arm. 

The 31-year-old British and Irish Lion was expected to return for Rounds 5 & 6 as the defending champions attempt to fight their way out of a tough Pool 1, but head coach Leo Cullen has issued an update which puts O’Brien’s return at between eight and 12 weeks. 

The flanker, who recently underwent a surgical procedure on the forearm injury sustained in Ireland’s victory over Argentina, may now not be available for Champions Cup action until the quarter-finals next March, if Leinster, currently trailing leaders Toulouse by two points, qualify. 

O’Brien missed all but two games of Leinster’s Champions Cup-winning campaign last season, when they won the trophy for a record-equalling fourth time, but he featured in the Irish province’s 52-3 home rout of Wasps and their dramatic 28-27 loss at Toulouse last month. 

Leinster centre Robbie Henshaw is also expected to sit out December’s Heineken Champions Cup double-header against Bath Rugby, after he sustained a hamstring strain in the warm-up before Ireland’s win over Argentina. 

The 25-year-old – who will be sidelined for between four and six weeks – has scored 11 tries in 38 European matches, including a second-half score in Leinster’s Round 1 victory over Wasps. 

However, Cullen was more positive about the fitness of flanker Dan Leavy, who has strained his neck. At present, he is only unavailable for the Guinness PRO14 clash with Ospreys on Friday night.