Warriors sit bottom of Pool Four after having lost their opening two European ties at home to Ulster and away at Northampton – despite some promising moments.
But tonight's match-up represents the first of a home-and-away double-header with the French Top 14 cracks which could turn their Heineken hopes around.
The big No.8, who will start on the bench tonight, is clear that Glasgow not only have to win, but claim a bonus point into the bargain, if they want to take the first steps towards European redemption.
Wilson said: "Without doubt this is an all-or-nothing affair. We have to win tonight and, for me, we need a victory with a bonus point.
"If we can produce that, then Castres will have their own momentum damaged and I think it would make it very difficult for them to progress.
"On top of that, it would provide an outstanding platform to go to France on Sunday week and double up on them.
"But all of our focus has to be on tonight. We have produced in patches over the first two ties, like the first 30 minutes at Northampton. Tonight it is going to be fully committed for the 80 minutes.
"But, by the same token, Castres have four points on the board and they will know that if they can beat us at Scotstoun that will set them up nicely for the return leg at their place.
"It would keep their hopes of catching Northampton in second place very much alive. So I think you could say that for both sides this is a must-win match."
Glasgow head coach Gregor Townsend has made three changes to the Warriors side which was hammered at Munster last weekend in the PRO12.
Joint-top scorer Tommy Seymour returns on the wing, Scott Wight is preferred at stand-off to Duncan Weir, and Josh Strauss starts at No.8 with Wilson benched.
Glasgow's new signing from Canterbury Crusaders, Sean Maitland, is set to make his debut from the replacements.
The need to win tonight's tie is glaringly obvious for Townsend and his plucky Warriors squad.
Whether it has been in PRO12 action in the opening-day trip to Ulster or at home to Euro champions Leinster, or in the two doomed opening Heineken Cup ties already mentioned, Glasgow have developed a knack of losing the games that really matter, the matches that can make a season.
Tonight's meeting with the Frenchmen, whose coaching team of Laurent Travers and Laurent Labit will be keen to bring European success to the Stade Pierre-Antoine in their final season in charge, is the ultimate fixture in that mould.
Victory would surely give Glasgow the confidence and belief to go to France in nine days' time and have a real go at the double over Castres.
That, in turn, would set them up for the PR012 1872 Cup double-header with arch-rivals Edinburgh.
Defeat would mean that yet again Europe is over before Christmas and the ignominy of finishing bottom of Pool Four beckons.
And Wilson is in no doubt where the game will be won or lost. He said: "Castres have the best scrum in the Top 14 and we have to take them on up front and take that away.
"Our scrum did not work at Munster last Saturday, but tonight it is an absolute must that it is back to its best. It's not an exaggeration to say this is easily the biggest game of the season so far."