Warriors will have only pride at stake, but Kellock is confident that will be enough to spark his side to claim their first win in four outings in Europe's top tournament.
The Glasgow lock is facing an enforced rest for the trip to France, but would have been unable to take part in any case due to a horrific gash down his left arm caused during the first clash with Castres.
But while that defeat meant Glasgow slipped to three defeats on the bounce for the first time under Gregor Townsend, Kellock is confident that not all is doom and gloom.
He said: "I think the big thing we have to do with the first tie with Castres is to keep it in perspective.
"We lost that game rather than them winning it and I believe if we can eradicate the errors that undid our efforts we can get something over there on Sunday.
"If you look at the games we have had with Northampton and Ulster prior to that, then we more than gave two of the best sides in the tournament a run for their money.
"Against Castres we know we did not perform to acceptable levels, but at the same time only lost out 9-6.
"There is absolutely no need to panic. Bottom line is that we need to fix what went wrong last time out and if we do that then Castres are in trouble.
"We have to produce a performance that puts it all together for the 80 minutes.That is the target for Sunday and there is real determination to do that."
Although the Warriors skipper would have missed Sunday's trip to France due to rest protocols, he may well miss the first leg of the 1872 Cup with Edinburgh at Scotstoun a week today.
Kellock revealed: "The gash down my arm is a nasty one and I am very lucky it did not go right down and into the tendon.
"It was caused by studs slipping down the arm, it was only when I looked down and saw the blood gushing out that I realised how bad it was.
"Hopefully I am a quick healer and it won't leave me on the sidelines for Edinburgh."
HE ADDED: "I know there has been a lot of talk over these new rest guidelines and, as a player, you just want to play every game.
"But I think these protocols are something that can put a few years extra on a player's career and that has got to be a good thing.
"On a personal note, I guess it is a plus that my rest came when I would have been out through injury in any case."
Kellock's talismanic influence will be sorely missed, but the Warriors skipper has no doubt that the second-row combination of Tim Swinson and Tom Ryder will provide Glasgow with crucial ball in his absence.
He said: "I think Tim and Tom have already proven that they are a more than decent partnership in our second row.
"They may have different styles, but they complement each other and they are two very determined boys.
"But right through the camp there has been a real determination to go over to Castres and produce something Glasgow Warriors can be proud of.
"If you look back to the likes of the Toulouse game when we went over there and beat them, no-one gave us a prayer for that one and we showed if we get it right we can beat anyone.
"So that is the type of performance we have to use as our benchmark on Sunday."