Seven-times French champions Lyon recorded a 2-1 home victory against Lille last week to revive their chances of a top-three finish but they still have a lot of work to do if they are not to miss out.
Lyon remain in seventh spot, although only four points separate them from third-placed Lille while they are three behind St Etienne.
"We are behind Saint-Etienne but the league is not over," the 20-year-old Lacazette told Lyon website.
"The fans are here to remind us that this game is a tradition. I think I played them once or twice a season since I was 12 and did not lose any games.
"But if we lose, our season will get a whole lot harder."
Lyon have a poor away record this season, losing eight of their 14 on the road, and they are in the unusual position of making the short 60km trip as underdogs.
"Saint-Etienne are the favourites. Everything works for them these days and we struggle away. We can be worried," Lyon chairman Jean-Michel Aulas told reporters.
St Etienne, who have not played in the European Cup or its successor, the Champions League, since the early 80s, hope their fans will help them take another three points to help them realise their ambition of re-joining Europe's elite.
"The game is not only about sport, it is also a historical and cultural confrontation. The fans will be fiery," keeper Stephane Ruffier told the club's website.
St Etienne are without midfielder Fabien Lemoine who is sidelined through an ankle injury.
The battle for the title between leaders Paris St Germain and second-placed Montpellier continues on Saturday with both sides away to clubs battling to avoid the drop.
"We will have to give everything. We will play against a resolute team," PSG fullback Siaka Tiene told a news conference.
PSG, who are hoping to clinch their first league title since 1994, are on 58 points, one ahead of Montpellier.
Carlo Ancelotti's side will be without midfielder Mohamed Sissoko after his dismissal last weekend at Dijon but Thiago Motta is back from suspension.
Fresh from knocking Inter Milan out of the Champions League,
Marseille are eight points behind third-placed