They were particularly poor away from home, winning only two of their five games, but Arsenal full-back Sagna insists anything other than victory is not an option.
"It's one of the biggest games I've played in because at the end you can go to the World Cup so we have to win it," he told Arsenal TV.
"I think France have just missed one (World Cup finals) so it would be a big shame to stay here. I don't want to think about it, I just want to play at the World Cup.
"We have to give more than we did in qualifying and if we do that we'll be fine."
The Republic have impressed under coach Giovanni Trapattoni, going through the group stage unbeaten and drawing twice with reigning world champions Italy.
Sagna expects the pace of the game to be like a Premier League match, and he will make sure his team-mates know exactly what is coming.
"It'll be a very intensive game and we have to be ready," he said. "There'll be a good atmosphere and they have good players but we (who play in the Premier League) know the players so we can talk about them to the other players.
"It'll be a crazy game. They (the Irish) are crazy about football and I expect them to run all over the pitch to give everything and in the away game as well."
France will be without playmaker Franck Ribery for the two-legged tie because of a knee injury but Sagna is optimistic they can overcome the blow.
"He can change the game and he's a very good player," said the 26-year-old. "He's a big loss for us but we have other good players and they'll want to show what they can do."
Meanwhile, left-back Patrice Evra has been told by Manchester United team-mate John O'Shea to prepare for "hell".
"O'Shea, he promised me hell at Croke Park," the defender told L'Equipe.
Evra has called on his team-mates to stand up and be counted and has implored France fans to get behind the team and the coach.
"We must stop hiding behind Domenech," he continued. "People who whistle are the same. They should not forget that he is a coach who must lead France at the World Cup."
France 6/4, Rep Ireland 13/8, Draw 2/1