Ulster have a major crisis on their hands after it emerged Ireland lock Dan Tuohy suffered a pulled calf muscle during the defeat to Northampton and will be out until the new year.
Tuohy was forced off near the end of the game and the diagnosis rules him for at least four weeks.
With skipper Johann Muller already sidelined for eight weeks with a fractured arm and Lewis Stevenson still not back following a knee injury, coach Mark Anscombe will be looking to back-row duo Iain Henderson and Robbie Diack to fill the void alongside Ravens skipper Neil McCombe.
It was a bad weekend for Ulster on all fronts in that they lost their unbeaten record this season, and the liklihood of being without Tommy Bowe for the rest of the season when the Ireland winger damaged his right knee.
Ascombe is expected to role out his best available side to face Leinster in the Pro12 this Friday night at Ravenhill, although there are also doubts over the availability of fly-half Paddy Jackson.
Bowe will undergo surgery later this week. Bowe's place in the Ulster team is now likely to be taken by Ireland's try-scoring hero against Argentina Craig Gilroy for Friday night's game.
Elsewhere, Wales international Lee Byrne could face a lengthy spell on the sidelines due to a back injury. The Clermont Auvergne full-back was hurt just before half-time of his team's Heineken Cup victory over reigning European champions Leinster in Dublin on Saturday.
The French club said 32-year-old Byrne had "suffered a fractured right pedicle of the fifth lumbar vertebra".
Byrne, who has won 46 Test caps and toured South Africa with the 2009 British and Irish Lions, is in his second season of a three-year contract with Clermont.
He was not part of the Wales squad that played autumn internationals against Argentina, Samoa, New Zealand and Australia last month, losing all four games.