Wallace, who had been a doubt to start the game, was forced off in the 52nd minute after catching his studs in the turf in a tackle.

With the last two rounds of Heineken Cup group action against Bath and Edinburgh to come, Wallace’s injury would be a major blow to the Ulstermen’s challenge to Stade Francais at the top of Pool 4.

Lions flanker Stephen Ferris was also nursing a sore shoulder while Willie Falloon also had to be withdrawn from the fray with a knock but neither injury is thought to be as serious as Wallace’s.

And coach Brian McLaughlin – although disappointed with his side’s performance – was delighted with his side’s resilience against their rivals.

“I’m really pleased that we played ugly and won,” he said. “Last week, we played exceptionally well against Leinster and got nothing out of it.

“In general our defence was good and certainly we knuckled down in the last 10 minutes under ferocious pressure and came away with the win so from that point of view I'm very, very happy.

“Usually when we don't perform at our optimum level, we lose. It was a step forward for us; it wasn't nice rugby, it was difficult conditions on the hard ground but we stuck at it and we've come away with four points.”