"Your next game is always your biggest, but this is do or die," said Harlequins boss Conor O'Shea. "We both want to win the game and we all know what we need out of the game.
"We have fought tooth and nail over the last few months to get ourselves where we want to be and it comes down to this game.
"The Heineken Cup is the pinnacle, it's what the players aspire to. Clermont have been one of the great sides in Europe over the last five years but they have never one it. This is their holy grail."
Clermont remain one of the favourites to lift this year's Heineken Cup having shown some formidable form in the group stages.
No side has made more successful carries or metres than Clermont in their year's competition and their scrum has once again been formidable. Their scrum success rate of 97% is better than any other side in the tournament.
Morgan Parra's early return from a knee injury is a huge boost but the French side will travel to Twickenham Stoop without skipper Julien Bonnaire. The France international faces six weeks to eight out of action because of a fracture to his right forearm. Clermont will also be missing scrum half Thierry Lacrampe, who is due to miss three weeks with a knee problem.
- Clermont saw off a resilient Harlequins side 23-16 in Round 2 at Stade Marcel-Michelin meaning that all three Heineken Cup meetings to date between the clubs have been won by the home side (Clermont W2) with the first two matches coming in the 1999/2000 pool stage.
- Clermont have made more carries (140) and metres (547) per game than any other club in this season's competition. They've also spent the most time in possession per game (20 minutes 58 seconds).
- Clermont's scrum success rate is 97%, a tournament high figure. Harlequins have won more scrums than any other side so far (35) and their win ratio is 90% (4th best).
- Clermont have made an average of 22 offloads per game so far - another tournament high.
- Sitiveni Sivivatu has made the most metres (417) to date with Mike Brown third in that chart on 321 metres. Chris Robshaw (57 - joint 2nd) and Sitiveni Sivivatu (56 - 4th) are among the top ball carriers going into Round 5.
- Naipolioni Nalaga is the joint highest try scorer with four going into Round 5.
- Sitiveni Sivivatu and Mike Brown are ranked sixth and seventh on the Amlin Opta Index respectively.
- Nick Easter is ranked as the fourth best forward based on the Amlin Opta Index this season, making 51 carries, 10 offloads and 29 carries so far.