Doubts remain over international forwards Peter O'Mahony (hip) and Donncha O'Callaghan (knee), while Keith Earls (hamstring), James Downey (hand) and captain Doug Howlett (shoulder) are also still in the treatment room.
"There's no doubt Clermont are roaring hot favourites and we're underdogs. You can either thrive under that tag or wilt away," said Penney.
"The best teams should be in the Heineken Cup at this stage and Clermont are certainly in that bracket. They've got real depth.
"We were going through their substitutes and you would be just wrapped to have them. They have an All Black 9, 10, 12 and 13 on the bench and Sitiveni Sivivatu starts on the wing.
"But we still have a lot of expectation from the Munster public and supporters, it's a double-edged sword. I don't want to say we believe we will beat them but we are going to go over there and give it a good crack.
"A game of rugby is such a dynamic one that on any given day an underdog can pull it off. It's 15 versus 15, we have a great referee in Nigel Owens and we just have to make sure we prepare well and perform."