After the Gunners' midweek heroics, they meet the rather more humble Os.
Leyton orient manager Russell Slade is under no illusions about the size of the task facing his side when Arsenal visit Brisbane Road on Saturday.
Slade watched in awe, along with everyone else on Wednesday night, as the Gunners came back from a goal down to beat Barcelona in the Champions League, but he insists his side are ready for what he describes as "the ultimate test".
He told the club's official website: "We're really looking forward to the game. It's a different challenge, against world class opposition.
"It's a great test - the ultimate test - but I don't think there's one player not looking forward to it. We've had a fantastic FA Cup journey and we don't want it to finish."
Orient have made it to the fifth round the hard way after battling wins against Championship sides Norwich and Swansea. But the east London side are already being written off in many quarters, though Slade believes they have a good chance of causing an upset.
He added: "It [the FA Cup run] might finish, and the bookies might suggest that it is finished before a ball is kicked, but we don't think so. We believe we still have that little window of opportunity to progress and we'll give it everything.
"We deserve this tie 200 per cent. To win away at Norwich and Swansea, who are flying high in the Championship, was an achievement, and this is now our seventh game in the competition."
Arsene Wenger: We will treat Leyton Orient like Barcelona
Arsenal manager Arsene Wenger is adamant his side will not underestimate League One Leyton Orient in Sunday's FA Cup fifth round tie.
The Gunners head to Brisbane Road on the back of their magnificent 2-1 victory over Barcelona in the Champions League but Wenger knows that will count for nothing on Sunday.
"We can gain more respect from everybody if we turn up on Sunday with absolutely full commitment. Then people will say this team is ready to have a real go and not choose the competition or the games," he said.
"When you are a top-level competitive man or team you go absolutely 100 per cent committed into every game.
"The media give more importance to some games than others but for us to win trophies we have to take a distance with that and be able to switch from one competition to another with exactly the same commitment."
He added: "We are hungry for success. Every time we go out we just want to win the next game. I personally believe we go for every single competition to the end.
"We have the hunger and the talent and are committed."From Wednesday we can get more belief. But Sunday is the FA Cup and we will have total focus and commitment because we want to be successful. We are involved in every single competition. That is why our destiny will be determined by our mobility for every game."
Midfielder Matthew Spring is a major doubt for the fifth round clash with Arsenal and will have a late fitness test on his calf. Adam Chambers is ruled out of the tie with a shin injury and is expected to be missing for another fortnight.
But otherwise Russell Slade has a near full-strength squad to take on the Gunners. Striker Jonathan Tehoue is pushing to be included in the starting line-up after getting the winner against MK Dons from the bench.
Two ex-Gunners - Ben Chorley and Jason Crowe - are in line to face their former club. Chorley was in the Arsenal youth team that won the FA Youth Cup in 2000 and 2001, while Crowe made three first team appearances under Arsene Wenger in the late 1999s.
Possible starting XI: Jones; Omozusi, Whing, Chorley, Crowe; Cox, Dawson, Daniels, Smith; M'Poku, Revell.
Manager Arsene Wenger has no new injury worries ahead of the trip League One Leyton Orient, though he may take the opportunity to rotate his squad.
Johan Djourou was a doubt after he injured his back in the 2-1 win over Barcelona but Arsene Wenger revealed on Friday that the Swiss international's knock had improved.
He will take his place in the squad alongside Theo Walcott who has recovered from a hamstring injury and is in contention for a start. Bacary Sagna could return to the first-team squad after serving a one match European ban on Wednesday night but Abou Diaby serves the second of his three match ban after being sent off against Newcastle.
Thomas Vermaelen (achilles) and Lukas Fabianski (shoulder) are the north London clubs only long term casualties.
Possible starting XI: Almunia; Sagna, Koscielny, Djourou, Gibbs; Rosicky, Denilson, Wilshere; Walcott, Chamakh, Bendtner.
Leyton Orient and Arsenal have met four times in the FA Cup with the north London club overcoming their east London rivals on every occasion.
The last time the two sides met was back in the 1977-78 season in the FA Cup, when the Gunners ran out 3-0 semi-final winners.
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