With Chelsea trailing Arsenal by four points in the league, conceding an away goal in the first leg and looking for a first win in 18 games against their north London rivals, his side are underdogs, Ranieri told a news conference at Arsenal's ground.
If Arsenal win "for us it is not unusual but if we win tomorrow for Arsenal it would be a bad moment," Ranieri said before his squad's final training session.
"This year Arsenal are one of the big teams not only in England but in Europe. They have been working four years minimum to achieve the (Champions League) final.
"Chelsea started this season...for us it is a bonus to get here," added Ranieri, who made wholesale changes to his squad after Russian Roman Abramovich bought the club last July and pumped 120 million pounds ($221.7 million) into new players.
The Italian coach scoffed at suggestions that last Saturday's 1-0 FA Cup semi-final defeat by Manchester United at Villa Park would affect Arsenal on Tuesday.
"They didn't want to fight 100 percent or they would have used all their players -- (Thierry) Henry first," Ranieri said.
Arsenal coach Arsene Wenger started with his France striker on the bench and Henry failed to score after he was brought on in the second half.
"Tomorrow you will see a different Arsenal,"Ranieri said.
The Italian, who has failed to beat Arsenal in his four years in charge at Stamford Bridge, including four matches so far this season, said he had no trouble motivating his players for the match.
FOUR GOALS
Striker Jimmy Floyd Hasselbaink, who has scored four goals in Chelsea's last two league games, said all his team mates were itching to get at Arsenal.
"It's not that we talk about it all the time but you can see it in each other's eyes," the Dutchman said. "We believe it's just a matter of time before we have a victory against them."
Despite his run of form Hasselbaink may not start on Tuesday with Ranieri, dubbed the Tinkerman, likely to shuffle his squad.
"I've done my bit but it's not up to me...if it was, yes, I'd play," Hasselbaink said.
Ranieri has four strikers to choose from with Romania's Adrian Mutu, Iceland's Eidur Gudjohnsen and Argentina's Hernan Crespo also fit.
"I think the team who stay the calmest, who have the most patience will win," Hasselbaink added.
Ranieri rued the goal that allowed Arsenal back into the tie at Stamford Bridge two weeks ago, earning them a 1-1 draw.
"But I like to remind myself and my players that in Europe we have won every away game and scored every time," he said.
Chelsea's fine away record included a 4-0 thrashing of Lazio in Rome and they have not conceded a goal on their Champions League travels.
Chelsea are hoping the 12 km trip across London will see them earn a longer journey in the semi-finals where they would face Real Madrid or Monaco, who meet in the principality on Tuesday with the Spanish side leading 4-2 from the first leg.
