Arsenal manager Arsene Wenger has warned his side an "average performance" against Napoli on Wednesday night could end their Champions League dreams.
The Gunners headed to Italy three points clear at the top of Group F, and a draw would be good enough to secure first place and with it seeding for the knock-out stage.
Even defeat could see Arsenal progress, depending on the final scoreline and also Borussia Dortmund's result in Marseille. It could also see them go out.
Wenger does not want any complacency against Rafael Benitez's men, who need victory to maintain their own hopes of qualification in what is set to be an intimidating atmosphere at the Stadio San Paolo.
"I see it as another game we want to win, and that is the only way we can approach the game," Wenger said.
"Benitez has a very big experience, is a very intelligent manager, so I know he will prepare his team well. The only way we can counter that is to be at our best and put in a good performance as an average performance will not be good enough tomorrow."
Wenger added: "For me the most important thing is to qualify. If we can finish top, it is even better."
The Arsenal boss expects his men not to be overawed by the hot reception which awaits them, having already produced smash-and-grab raids at equally intimidating away venues earlier in this current Champions League campaign.
"That is part of the big games, we know how to deal with that because we have that everywhere in Europe," Wenger said.
"When you go from Fenerbahce to Dortmund, you are used to these kind of atmospheres."
Wenger does not want his team to dwell on the frustration of not being able to hold out for victory over Everton on Sunday, which would have extended their lead at the top of the Barclays Premier League to seven points.
Arsenal now head into a run of six matches in 22 days.
Wenger's squad will have little time to recover when they travel back from Italy before tackling Manchester City at the Etihad Stadium on Saturday lunchtime.
Then Arsenal have a showdown with Chelsea on December 23 as the festive fixtures get into full swing - with the small matter of a north-London derby against Tottenham in the FA Cup third round on January 4 further away on the horizon.
Wenger remains fully focused on the immediate challenge in front of his side.
"Tomorrow's game certainly (is decisive) as it is to be in the Champions League or not. The two other (Premier League) games not definitely as we are five points ahead and overall the (English) championship is a marathon," he said.
"We will be in the race, no matter what happens. We will show our strength hopefully, but tomorrow is a decider, that is for sure."
Wenger added: "The attitude of the players for me is absolutely focused, ambitious and that is what pleases me very much, because it shows the players want to do well until the end of the season."
Bacary Sagna continues to recover from a hamstring problem, so Carl Jenkinson looks set to deputise at right-back again in Naples.
England forward Theo Walcott, meanwhile, is pressing for a place in the starting line-up having been used as an impact player from the bench after his return from minor abdominal surgery.
Arsenal are likely to come up against Gonzalo Higuain, the Argentina forward whom Wenger tracked before he signed for Napoli from Real Madrid in a £34million summer move.
Wenger is not concerned with what might have been, as Arsenal went on to smash their transfer record to land German playmaker Mesut Ozil on transfer deadline day.
"There were a lot of statements that were not true about Higuain, but he has joined Benitez, is in good hands and shows he is a great striker," said Wenger.
"But we have (Olivier) Giroud who shows as well he is a great striker."
Wenger added: "Higuain is a player you have to keep quiet as he is of course very dangerous, so the more we can play outside the box the easier it will be for us to keep him quiet."