Bayonne and London Wasps clash in potential back-to-back Pool 4 deciders with captain and international flanker Remy Martin accepting these will be the acid tests.
Bayonne and Wasps are level on nine points apiece but the French club top the group courtesy of having scored two more tries than Wasps.
"As it stands we are in a good position in the Amlin Challenge Cup but, having said that, we can't say we have met the strongest team yet," said Martin.
"London Wasps are definitely the team to beat and we will have to double our efforts because we face them twice in a matter of one week.
"We'll have to stay focused and committed throughout the two encounters. That will require a lot of energy and whatever the result in Round 3 we must keep up the hard work and do our best again for Round 4 - first and second places are at stake.
"Wasps have already shown their fine European pedigree as double Heineken Cup and Amlin Challenge Cup winners and they will be up for the challenge again this season and determined to climb up the ladder and return to the Heineken Cup at all costs for next season. Like all English squads in this tournament they will give it 100%."
But the teams had totally different domestic tournament preparations for the return of Europe. While Wasps won 24-22 at home to Leicester Tigers to consolidate their fifth spot in the Guinness Premiership, Bayonne went down 34-10 at Stade Français Paris.
"It is vital to finish first in your Pool and qualify for the quarter-finals so we are in for a superb game of rugby," said Martin. "Because, as far as we are concerned, we don't want to botch either the event or our performance and with that the chances to do well in the competition.
"That back-to-back series will be decisive for us and we'll see whether we can stick to our ambitions.
"I played against them before in the tournament and I was with Stade Français and they smashed us on two occasions in the season they ended up lifting the trophy.
"They are a good example of a team who can compete well in both European tournaments and who can commit in the same fashion with the same goals each year to aim for the top.
"Whether it is the Amlin Challenge Cup or the Heineken Cup, I think it's good for all the participating clubs to pit one's strength against big teams - it gives you another dimension and perspective.
"And despite the fact that Bayonne are not in a good posture in the Top 14, it doesn't mean that we will do badly on the European stage.
"That remains an avenue in which we can still hope to do well and we will stick to our goal in that respect no matter what happens in our domestic championship.
"The European matches are important to win because it is vital for your confidence and for the progression of your players and it benefits the club records as a whole."