Ex-Arsenal midfielder Emmanuel Petit believes his former side could hold the psychological upper hand over Barcelona in the Champions League last eight tie.Outplayed by holders Barcelona for much of the first leg at the Emirates, Arsenal came back to secure a 2-2 draw. [LNB]"Arsenal have nothing to lose," Petit told BBC Sport ahead of Tuesday's game. "If I was Arsene Wenger I'd tell them that they're on the verge of history. [LNB]"Barca are champions and favourites and have everything to lose." [LNB]Arsenal have not won a trophy since lifting the FA Cup in 2005, but Petit believes that advancing past Barcelona would fully vindicate Wenger's long-term strategy of focusing on developing young players rather than bringing in big-name signings. [LNB]"If Arsenal can win against Barcelona it will probably be the best result in the club's Champions League history," said Petit, who first played under Wenger at Monaco after joining the club as an 18-year-old.[LNB] If Barca play intelligently, you fear the worst Ex-Arsenal midfielder Emmanuel Petit "If Arsenal can beat the best team in Europe, a team which cost millions to build, that will send a message to everyone that you can build the perfect team to beat the biggest team in Europe and win titles." [LNB]However, Petit concedes that Arsenal will start Tuesday's second leg at the Nou Camp as overwhelming underdogs, comparing the task facing Arsenal to climbing Mont Blanc. [LNB]Barcelona outplayed Arsenal for the first hour and in a memorable opening 25 minutes might easily have scored three goals, only to be denied by some superb goalkeeping by Manuel Almunia. [LNB]Second-half goals by Zlatan Ibrahimovic, who misses the second leg due to a calf injury, put Barcelona 2-0 ahead, before a Theo Walcott goal and a Cesc Fabregas penalty completed an inspired Arsenal comeback. [LNB]"I think they have maybe a 30% chance to do it," said Petit.[LNB]Messi had a quiet game in the first leg, but has scored 26 league goals"Arsenal will be without William Gallas and we saw he was missed on both goals Barca scored. They'll also miss Cesc Fabregas - those are two big blows." [LNB]Lionel Messi had a relatively quiet game in the first leg and Petit warned Arsenal that was unlikely to happen again. [LNB]"The Nou Camp pitch is much bigger than the Emirates," said the former World Cup winner with France. [LNB]"We didn't see much of Lionel Messi in the first leg but in the return Arsenal will have to score, so they will inevitably give the likes of Messi more space. [LNB]"It will be very difficult to find the right balance between attacking and defending and that's why I think it will be a huge, huge, sensation if Arsenal can qualify. If Barca play intelligently, you fear the worst." [LNB]Even if the odds are stacked against Arsenal, Petit still sees some green shoots of optimism for his old club, despite the absence of Fabregas, who cracked his right fibula after colliding with Barca defender Carles Puyol when he won the penalty. [LNB]"I've seen Arsenal play very well when Fabregas is not in the team," said Petit, who helped Arsenal win the Double in 1998. [LNB]"When Fabregas plays he is always asking for the ball and every ball comes through him. That's quite easy for an intelligent team to defend against, as we saw against Manchester United, Chelsea and Barcelona. [LNB]"If you stay true to your philosophy - keeping the ball on the ground, movement, passing, speed - then it doesn't only depend on one player." [LNB]And Petit pinpointed Samir Nasri as the ideal replacement for Fabregas. [LNB]"Nasri is better when he plays in central midfield," said Petit, who moved to Barcelona from Arsenal in 2000. [LNB]"He can do it. He has stepped up physically and mentally. He's not the same player he used to be, he realised what he needed to do to play at the top level. [LNB]"He has improved a lot over the last few months and I'm sure he can play in central midfield."[LNB] How much will Barcelona miss Ibrahimovic? Barcelona are not invincible at home in Europe and back in October Russian side Rubin Kazan pulled off one of the great Champions League shocks when they beat Pep Guardiola's side 2-1 at the Nou Camp. [LNB]Barca will also be without some key players on Tuesday, with key defenders Puyol and Gerard Pique suspended and the injured Ibrahimovic also ruled out. [LNB]"Rafael Marquez and Gabriel Milito will probably play in central defence and that could allow Arsenal to do something because those two don't play together often," added Petit. [LNB]"Those positions are very important for the team, it's the spine. They may not have the understanding that Puyol and Pique have." [LNB][LNB]Read more of Petit's thoughts on Arsenal's Champions League match with Barcelona on Tuesday when the BBC Sport website will provide a statistical analysis of Barca's strengths and weaknesses and how the Gunners might win the second-leg tie.