London: A routine FA Cup fifth round replay against League One side Orient on Wednesday has been transformed into a challenging test of Arsenal's character and nerve following their League Cup final defeat at the hands of Birmingham City.
Arsene Wenger's side had been widely tipped to collect their first trophy since 2005 against their Premier League rivals but stumbled in agonising fashion, losing out to a late goal following a horrible defensive slip.
The inquest started immediately at Wembley with the Gunners' mental strength placed under scrutiny as well as the potential impact such a disappointing defeat might have on the rest of the campaign.
Wenger's side remain in contention for three trophies with the Orient clash kick-starting a run of three games that will affect their hopes in the FA Cup, the Premier League and the Champions League.
Yet while the return meeting with the League One club was assumed to be little more than a minor obstacle on the way to a quarter-final meeting with Manchester United at Old Trafford after the first game, it will now be approached with caution.
"Of course (it will be difficult) but that is part of our job, to pick ourselves up," said Wenger.
"We have massive challenges in front of us and we do not want to miss them because of this final minute of the game.
"This team has produced a fantastic season until now so we need to support them, try and get behind them and pick them up. Until now they have been fantastic and they have to finish the season as well as possible."
The reaction of centre-back Laurent Koscielny and keeper Wojciech Szczesny will come under particularly close examination.
It was the lack of communication between the pair that led to Birmingham's winner although Wenger may give the duo breathing space if he elects to make wholesale changes as he did for the original tie.
Robin van Persie will definitely miss out after injuring his knee in the final while Theo Walcott and Cesc Fabregas will again be missing.
"Big games are decided by whoever makes the mistakes and unfortunately we made a big one," Czech midfielder Tomas Rosicky told Arsenal TV online.
"We have to pick ourselves up immediately. We have a game on Wednesday and we have to perform.
"The season doesn't finish now. We are still in a good position in other competitions. We have to forget this and concentrate on other games now.
"Leyton Orient is a very important game and we want to go through to the next round of the FA Cup."
Jonathan Tehoue's late equaliser that set up this replay provided one of the stories of the fifth round although Orient manager Russell Slade draws little comfort from Arsenal's troubles.
"It will make them more resilient - they are still fighting on three fronts. It would test their mentality, but they have such a good group.
"It would be nice to hit them early but it is a really tough ask. I don't know how many chances we are going to get.
"But what I do know that we have such good spirit that it won't be through the lack of having a go."
Orient's prospects haven't been helped by Tehoue suffering a migraine 48 hours before the game and Slade admitted he may miss out on the trip to the Emirates Stadium.
"He looked very poorly this morning when he went to see the doctor," added the manager.
"We are hopeful he will be back training tomorrow but we are not sure."