Cardiff started with an impressive win in Bourgoin before going down 21-17 to twice-European kings Leicester Tigers in front of a crowd of 26,645 at the Millennium Stadium, and a second home defeat would almost certainly mean the end of their Heineken hopes.
"After our win at Bourgoin at least we picked up a losing bonus point in our defeat by Leicester Tigers and we are still in there with a shout of qualifying. It is all in our hands.
"We have got a massive hurdle to clear," admitted the former New Zealand back-row forward.
"Munster proved they were the best side in Europe last season by beating Biarritz in the final and they have won their opening two matches in this season's competition so they are very much a form side.
"Their top players were in good shape in the autumn internationals series so as a team they will be a very hard prospect for us on Sunday.
"What is clear for anyone to see is that Munster are a very committed side. Fly-half Ronan O'Gara directs their game plan and he is a key man for them."
"We are through to the knockout stages of one tournament (EDF Energy Cup), so that is a great morale-booster, but playing back-to-back matches against the Heineken Cup champions is a massive challenge,"
The Cardiff club team and Munster have met on three occasions in the Heineken Cup, the last time being in 1998, with the score standing 3-0 to the Welsh outfit.
The Blue and Blacks won 48-18 in 1996-97 and 43-23 the following season, both at home, before notching up a 37-32 away win in Cork.
But this clash is the first time the Blues regional entity has clashed with Munster and Rush is under no illusions about what his side has to do to win,
â00We just have to worry about ourselves and not the opposition. Our biggest difficulty has been not following through with our game-plan clearly enough.