Rennes coach Frederic Antonetti believes his side and Celtic are fighting for their Europa League lives when they clash in Glasgow on Thursday.
The two sides have only two points each in Group I and are behind Udinese and Atletico Madrid.
Asked if defeat at Celtic Park would end his side's hopes, Antonetti said: "Mathematically not, but psychologically, probably, yes.
"I think both teams will really want to win. It is an important game."
Celtic are unbeaten in five European home matches but are 12 points behind rivals Rangers in the Scottish Premier League after a lacklustre start to the season, including last weekend's 0-0 draw at home to Hibernian.
"It would be a massive, massive achievement to be able to beat Celtic at home," said Rennes' coach.
"Celtic is a big name on the European stage, so it's a massive challenge.
"We're not going to just turn up and watch them play. We're going to come here and try to win the game."
Antonetti played down the relevance of Celtic's domestic troubles, which have put manager Neil Lennon's position under pressure.
"The two competitions are really different," said the Italian.
"Quite often you see a team struggling in the league and doing quite well in Europe."
Rennes are yet to win a match in the group and drew 1-1 with Celtic in France, but Antonetti is bullish about his side's chances.
"We're proving we can win games," he insisted. "We may be lacking a little in experience, but we're getting there - we can win.
"If you look at the three games we've played so far, we could have ended up with nine points.
"We were close, but we just didn't manage to do that.
"What we need to do is just get that little bit extra so that we do get the three points."