Jamie Roberts insists Cardiff Blues' double-header against Edinburgh will "make or break" the region's season.
The Blues take on Edinburgh on Friday night with the two sides meeting again at Murrayfield a week later.
Both sides go into the Cardiff City Stadium clash with unbeaten records after their opening two European matches.
"The next fortnight in the Heineken Cup is probably the most important of our season," insisted the Wales centre.
"And we need to make sure we are on the money on Friday against a very good Edinburgh side.
"It is a must-win. This fortnight will make or break our season."
"[Edinburgh] have got talent across the park and [Tim] Visser is very dangerous on the wing and certainly a player we need to contain.
"But we have the quality and, if we are sharp, we will win on Friday."
Roberts conceded that preparation for the game had not been ideal.
First the Blues suffered a 52-9 record Pro12 defeat at the hands of Leinster in Dublin a day before eight of the region's players were involved in Wales' 24-18 defeat at the hands of Australia at the Millennium Stadium.
"The boys out in Leinster lost quite heavily and they will be looking to put things right," said Roberts.
"Us international boys were massively disappointed to lose to Australia.
"I suppose there is no game [against Edinburgh] of more magnitude really to try and put things right.
"The record defeat [against Leinster] was bitterly disappointing. Certainly watching the game the night before we played Australia it was pretty brutal.
"There is no better game to turn things around than the most important game of our season.
"Edinburgh have won the first two games in the Heineken Cup, as have we [against London Irish and Racing Metro].
"Whoever is victorious over the next fortnight will go into rounds five and six with their destiny in their own hands."
The Blues have beaten the Scots in their last five encounters, but Roberts is not relying on recent history.
"It's a little bit of an advantage, but form goes out of the window with the Heineken Cup. Anything can happen," he warned.
"Edinburgh play a great brand of rugby. They have a lot of talented individuals and they play a game people enjoy watching, and they have a lot of international-quality players in their side.
"We know we have to be on the money come Friday night if we are going to beat them and hopefully go up to Murrayfield and do the same. It's massively important to us."