Arsenal forced to focus on defence
Arsene Wenger's side produced a stirring comeback to win 2-1 in the last-16 first leg at Emirates Stadium, when Van Persie and Andriy Arshavin struck late goals to shock a Barca team who let them off the hook.
Since that high, however, Arsenal have gone through the full gamut of emotions.
Their League Cup Final defeat by Birmingham City blocked their easiest route to long-overdue silverware and after being given optimism in the Premier League title race by Manchester United's loss to Chelsea, were promptly held 0-0 by Sunderland.
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Wenger was furious after his side failed to beat Sunderland and his mood was not helped by an injury to Jack Wilshere that threatens to keep the precocious midfielder out of Tuesday's clash.
"Wilshere has an ankle problem and we'll wait until Monday or Tuesday to see if he's back," Wenger said, though Wilshere said on Sunday he was optimistic about playing.
Cesc Fabregas missed the Sunderland match with a hamstring injury but Wenger is optimistic he will be available.
While the absence of forwards Walcott and Van Persie is a blow, Wenger believes it is the efficiency of his team's defending that will be crucial.
Last year, Arsenal were crushed 4-1 in a Champions League quarter-final second leg at the Nou Camp, after a 2-2 first-leg draw, when an irresistible Lionel Messi scored all four goals.
"It will be very important for us to defend well because when you go to the most effective attacking team in the world, you want to have your best defenders available," Wenger said.
"We will look to defend well and attack well. We are not a team that will refuse to attack, we know that." Barca have recovered from the defeat in London to string together four consecutive victories and consolidate their place on top of La Liga.
They have not conceded a goal in their last three outings, but they have lost the swagger they showed earlier in the campaign and must make defensive changes against Arsenal.
Captain Carles Puyol has failed to recover from a knee injury and with Gerard Pique suspended, coach Pep Guardiola, who is struggling with acute back pain himself, will have to field an unfamiliar back line.
Eric Abidal and Gabriel Milito could step into the breach, though goalkeeper Victor Valdes has recovered from injury and returned in their 1-0 home win over Real Zaragoza on Saturday.
"If we maintain our personality, we'll be halfway there," midfielder Xavi told the club's television channel. "We are at home, we are the favourites and with the help of our fans we'll get through to the next round."