"Northampton have got control of the group at the moment, but things can change very quickly. Sunday is a must win game for us and we also have to ensure they come away with nothing.
"Losing up there was a big dent to our ambitions, but it isn't terminal. We have got to play better to give ourselves a chance.
"We knew the scrum would be tough, but their line-out caused us even more problems. There were moments when we got field position, and looked as though we could be dangerous, but then lost our line-out ball.
"We have got to sort it out ourselves and we must work on our line-out this week. There were individual errors and wrong calls and Courtney Lawes won three of our throws and didn't even have to move. It meant we had to play from deep all the time, and we didn't have any momentum, but we still pushed them at times.
"They are probably the strongest scrum in Europe, right up there with the big French packs, and sometimes we struggled in that area - we know it's again going to be a weapon for them.
Meanwhile, fellow Welsh region Newport Gwent Dragons may be out of the reckoning for a quarter-final place after three successive defeats in Pool 6, but acting skipper Ashley Smith isn't prepared to give up on the second half of the campaign.
"We will target Sunday's game against London Wasps and look forward to it," he said. "This is what the Heineken Cup is all about - going to places like Wasps and Toulouse and playing against top players.
"It's great to play against some of the best players around and it will be no different if Riki Flutey is fit to play again on Sunday.
Smith cracked the Wasps defence to score his side's only try in the 23-16 "home" defeat at Cardiff City Stadium andfirmly believes the Dragons could have taken more out of the game.
"The last 20 minutes we were stuck in their 22. We had plenty of possession but we couldn't get the points," he added.
"But there were a lot of positives to come from the game and we showed we can stand toe-to-toe with teams like Wasps. We had enough territory and possession to win the game. They showed how clinical they can be by taking their tries and that is how we want to be."
And Dragons coach Paul Turner is hoping his players will have learned from their mistakes in not grasping an opportunity to pick up a major scalp in the first leg.
"We played some of our best rugby of the season and I want the team to carry that into the return on Sunday. We were outstanding as a team, but we were still beaten," said Turner.
"They are a good side, but no different to the other top English sides. You have to muscle up to them, be patient and take your chances when they come - we didn't do that in the first game and we need to learn from those mistakes."
While Wasps are hoping England and British & Irish Lions centre Riki Flutey may be fit to return to action this weekend, the Dragons will definitely be without tight head prop Nigel Hall, who ruptured the Achilles tendon in his left leg and are sweating on the fitness of outside half Jason Tovey, who injured his knee in the second half last weekend.