USA international fly-half AJ MacGinty will almost certainly miss Bristol Bears' trip to La Rochelle on Saturday to further stack the odds against the English side in their bid to make the Champions Cup knockout rounds.

Bristol were beaten 35-12 by Leinster at Ashton Gate on Sunday with MacGinty forced off the pitch with a rib injury in the first five minutes after a big tackle from Garry Ringrose, which saw centre Benhard Janse van Rensburg move across to stand-off where he held his own but struggled to provide the fluidity in attack that MacGinty has this season.

READ MORE: Bristol Bears player ratings from Leinster defeat - 'A dominant display'

Lam said: "It was a huge disruption to us and our game losing AJ so early. BV just said to me, ‘Coach, I can do 20 minutes covering fly-half, but maybe not 70 minutes.’ His loss has a big effect on what we do. I could see our shapes and patterns were off because AJ and BV run a lot of that. We couldn’t play our shapes as fluidly as normal.

MacGinty's absence from the squad leaves a bit hole in the side with Lam's 'who back-up options at 10, full-back Max Malins and inside centre James WIlliams, both sidelined with knee and pectoral injuries respectively.

Lam continued: "We have now lost AJ, Max Malins is our second 10, Jimmy Williams is out third 10. AJ could be struggling for this weekend, he got hit hard in the ribs. The HIA was based on him getting a bit of whiplash but that was clear, so it is more his ribs. So now we have got young Sam Worsley in our academy who will have to step up.

"We are right down to the bottom of the barrel with 10s. AJ had played three tier two Test matches this Autumn with the USA and we have been told he needed to be rested this weekend anyway so we are really scrambling with our first, second and third choice out."

Worsley started at fly-half in Bristol's Premiership Rugby Cup wins over Bedford and Ampthill, as well as facing Australia A, in a series of solid if unspectacular displays.

Despite the Bears' shortage of options in the key position for the tough away fixture against two time champions La Rochelle, and then potentially away at Leicester Tigers the weekend before Christmas, Lam remains confident in his decision to go with a smaller senior squad this season as the club have cut their salary spend. He said: "I don't want quantity of players, I want quality. We would be okays is Max Malins and Jimmy Williams hadn't both taken a double hit against Bath and suffered long-term injuries.

"Max Malins should be back for December 27, so we have got a few more games to hang in there. Jimmy Williams should be back the week after that as well. There is a group of them, Noah Heward as well, Joe Batley and Josh Caulfield in the second-row, they should all be back around Christmas and New Year as well."

After an impressive scrummaging display against Leinster's all international front-row, Lam is hoping there won't be problems on that front against La Rochelle despite the game ending with uncontested scrums after replacement tighthead Lovejoy Chawatama was told to come off for a HIA.

Lam explained: "The mouthguard sensor went off. LJ didn't feel like anything was wrong. Don't get me wrong, safety is the most important thing, but he was bemused. So he had to come off and Max Lahiff had frozen up having come off earlier and his Achilles was feeling tight. We have already lost George Kloska for a couple more weeks, so we weren't going to take any risks with Max."

Returning England star Ellis Genge also limped off the pitch seemingly in discomfort early in the second half on Sunday but Lam was quick to alleviate fears around his key loosehead leader.

He said: "The calf that he tore last year just cramped up by the medics are confident that he should be okay."