Toulouse must win at Kingsholm on Friday night to qualify as the winners of pool six and secure a probable home quarter-final - otherwise Harlequins can snatch top spot with a victory over Connacht.
Gloucester's campaign ended last weekend with a defeat at The Stoop and they cannot drop down into the Amlin Challenge Cup either.
Director of rugby Redpath was frustrated but he has named his strongest available side and fired his team up by labelling Friday's clash a once-in-a-lifetime opportunity.
"To bring Toulouse back to Kingsholm on a Friday night is probably one of the biggest games you'll get in club rugby for a Gloucester player," Redpath said.
"It's a great opportunity for our players to go toe-to-toe with one of the very top teams in Europe. It's a reputation game and a chance to shine."
But Toulouse are four-time European champions and Guy Noves, the man who masterminded all those victories, relishes challenges like that laid down by Gloucester.
"We know we must come back from Gloucester with the win," he said.
"We are all aware how important this game is and we know that if we lose we can be eliminated and if we win we are qualified.
"I love these kind of games. After 20 years at the club, I have been involved with a lot but I love decisive games like these.
"Gloucester are eliminated but they caused us problems in the first game especially at the scrum but they can also score fantastic tries which we have seen already."
Toulouse are led by France captain Thierry Dusautoir and feature an array of stars including Clement Poitrenaud, Maxime Medard and the destructive prop Census Johnston.
Even if Toulouse win Harlequins know that a victory in Galway should be enough to secure them a quarter-final place as one of the best runners-up.
The Aviva Premiership leaders tackle a Connacht side who have not won in 14 games.
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