Munster are bidding to reach the knock-out stages of the Heineken Cup for the seventh successive season with coach Alan Gaffney declaring their back-to-back Pool 4 fixtures with Castres Olympique are "critical" to extending that record.
"Those home and away head-to-heads with Castres are massive matches for us and, if we finish in front of Castres after those games that will be huge for us in attempting to qualify for the quarter-finals," said Gaffney.
"But it is going to be tough, very tough. Castres are extremely strong up front and, with players like Richard Dourthe in the centre, they can pose some real problems behind the pack. We know a fair bit about Castres and they certainly were busy in the summer, recruiting in a big way.
"They brought in something like 10 new quality players, such as Paul Volley, Yannick Delaigue, Mark Denney and Bradley Fleming, with plenty of international experience among them.
"Castres are going strong in the French Championship and it is going to be extremely difficult for us over there on Friday night. I am not making any excuses but we only get our international players back tomorrow and we travel to France on Wednesday so it is not the greatest preparation for a huge match."
And Castres Olympique have got their own "inside man" in former Irish international prop Justin Fitzpatrick - who made 32 Heineken Cup appearances for Ulster, including their 1999 Cup final triumph over Colomiers - to give them the lowdown on Munster.
"The game against Munster is going to be massive," said Fitzpatrick. "In today's Heineken Cup there are no easy games, even in the Pool stages but, with probably only one team from our group going through, the clash against Munster is critical for both sides.
"The quality of Irish rugby in constantly improving and with no away team ever winning a Heineken game at Thomond Park, it is vital that we come away with a win at Pierre Antoine.
"Munster have consistently reached the quarter and semi-final stages of the tournament and are serious competitors. They have a strong front five and I'm looking forward to playing against John Hayes, who had a fantastic game for Ireland against South Africa.
"They also have a great set of backs with the likes of Ronan O'Gara, Christian Cullen, Rob Henderson and John Kelly. The fact that they have provided so many players to the Irish team this month and are still winning in the Celtic League without them shows what strength in depth they have in their squad.
"There is a great deal of pressure in the French domestic league this season. There are an enormous number of games and the added pressure of the reduction in league size emphasises the problem. The Top 16 doesn't give us any easy games and the French pride and desire to win, particularly at home, makes the domestic competition very high pressure and hard work. We can't afford to look too far ahead and are concentrating on one game at a time."