Arsene Wenger believes Arsenal's Champions League double-header against Borussia Dortmund will be "decisive" in the race to qualify from Group F.
Wenger's side host last season's runners-up on Tuesday before heading to Dortmund for the return on matchday four.
are currently top of their group following back-to-back wins over Marseille and Napoli.
Wenger knows another three points on Tuesday will leave Arsenal in pole position to reach the knockout stages, but he is also well aware that Dortmund could deliver a major blow to his side's qualification hopes.
"Dortmund have grown a lot and they look a different proposition now, maybe they were a bit impressed by us in the first group games when we met them in 2011, but this time they have gained confidence," Wenger told UEFA.com.
"I feel we are stronger as well this season, so I think it will be very interesting.
"It is already a very important tie because usually matchday three and four usually are decisive, so that could be the key for us to qualify."
Wenger, whose side are two points clear at the top of the Premier League following Saturday's 4-1 win over Norwich, has a wealth of options to ponder in midfield, with the return to match fitness of Santi Cazorla following an ankle injury.
Aaron Ramsey started on the bench against Norwich but replaced Mathieu Flamini just before half-time after the French midfielder suffered double vision following a clash of heads with Alex Tettey, leaving him rated as doubtful for the Borussia tie.
"We have a squad that is, number and quality wise, very, very good. After that in January we are not desperate (to buy) now," Wenger said.
"If there is a good opportunity (to buy), why not? But if you know who is out injured now, they will come back in November, the beginning of December, then you have a really massive squad.
"With the number of competitions involved, everybody thinks they have a chance to play. That is what is the most important. As long as you fight for things, everybody keeps the focus."
Wenger also revealed England winger Theo Walcott will need a couple more weeks of recovery time following a minor surgical procedure on an abdominal problem.
"Theo had a set-back on Thursday. He had to stop, to jog again, I don't think we will see him against Dortmund, nor Crystal Palace nor Chelsea," he said.
"He is at least two weeks away now."
Despite their impressive 3-0 drubbing of Marseille in their last Champions League match, Dortmund arrive in London low on confidence after labouring on occasions in the Bundesliga this season.
They ground out a 1-0 win against Hanover on Saturday, with Germany winger Marco Reus netting a penalty after four minutes.
Dortmund coach Jurgen Klopp conceded his side weakened as the game went on, allowing Hanover opportunities to snatch an equaliser, but he expects them to be more dynamic against Arsenal.
"We should be a step further on Tuesday, we know we can play better football (than we did against Hanover) and we will too. I have a good feeling," said Klopp, who will be absent from the bench at Arsenal as he completes a two-game suspension for verbally abusing the fourth official during his team's loss to Napoli.
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