Ulster second rows Matthew Dalton and Iain Henderson have been ruled out of Friday’s Challenge Cup opener against Racing 92 (20:00 GMT).

Dalton picked up a knee injury during last weekend’s United Rugby Championship win over Benetton having replaced captain Henderson just prior to kick-off.

Henderson withdrew minutes before kick-off after a back spasm in the warm-up, and while Ulster said he was a doubt for Friday’s game, attack coach Mark Sexton later confirmed the experienced Ireland lock is unavailable.

“Hendy’s has had a back spasm last week so he’s out, Dalts has hurt his knee, so a couple of second-rows injuries,” said Sexton.

Cormac Izuchukwu – who has not played since early October – is also a doubt with an ongoing foot problem, but Sexton does not feel the injuries add up to a “crisis” with head coach Richie Murphy still able to call upon Charlie Irvine and Joe Hopes.

“I know they’re going to be big losses to us, but Charlie and Joe are brilliant young players and it’s brilliant that they’re going to get an opportunity,” added Sexton.

Hooker Rob Herring is also a doubt with an ankle problem he sustained after coming off the bench in the Benetton game.

With Michael Lowry having missed the Benetton game, Instonians full-back Bradley McNamara has joined the squad as injury cover after recently impressing in Ulster A’s win over Connacht Eagles.

“He was one of the standout players on the pitch,” said Sexton.

“His attack was brilliant that day which was brilliant to see. He’s very elusive, he has a good swerve, good passing and running game. We’ll keep a close eye in here now for the next couple of weeks.”

Australia prop Angus Bell could make his debut after arriving in Belfast last week.

“He trained today and trained very well so we’re hoping that he’ll be involved,” said Sexton.

He added: “He seems like a great fella, great character, and he can certainly move on the rugby pitch so I think we just need to get him the ball and let him go.”