However, van Persie's loss has been slightly tempered by a positive update on captain Cesc Fabregas, who could be fit to face the Spanish champions in next Tuesday's round of 16, second leg showdown at the Nou Camp. "Unfortunately, we had bad news on the scan and Robin will be out for the next three weeks for sure," Wenger told Arsenal TV Online. "It could be longer. The shortest delay we can imagine is three weeks, so he is definitely out for Barcelona. "Cesc is looking possible [for that game]. He is making quick and good progress. It is possible." Losing van Persie is a huge blow to Arsenal's hopes of progressing into the Champions League quarter-finals. The in-form Holland striker sustained the injury in the act of scoring Arsenal's equaliser during Sunday's 2-1 Carling Cup final defeat by Birmingham. The goal was his 13th in 11 games, a haul that includes the equaliser against Barcelona in the first leg, which the Gunners edged 2-1. Events at Wembley could yet prove pivotal in Arsenal's push for silverware, which has now been reduced to three fronts. Not only has the result enhanced doubts over their temperament as they seek to lift their first trophy since 2005, but they have also lost Van Persie for a critical stage of the season. Furthermore, what impact the blunder between Laurent Koscielny and Wojciech Szczesny that gifted Birmingham their late winner has had on the duo's confidence has yet to be discovered. Arsenal's squad face a real test of character as they attempt to rally themselves from a hugely dispiriting loss. The manner of their response in tomorrow night's FA Cup fifth round replay against Leyton Orient at Emirates Stadium will be scrutinised closely. With matches continuing to arrive at a frantic rate, Wenger will freshen up his team, his hand partly forced by injuries to two further players. Alex Song incurred a knee problem against Birmingham and will sit out the Orient game, but should return for Barcelona. Koscielny is nursing a minor hamstring problem and will be rested for the replay. Manuel Almunia will start in goal, with Szczesny on the bench, and midfielder Abou Diaby is expected to feature. "Alex Song has a knee problem. From his scan we had good news, it is only blood from a kick on the outside of his knee," said Wenger. "He is out for Leyton Orient and has a very small chance for Saturday. But he has a good chance for Barcelona. "Koscielny has a tight hamstring. There is a little bit of fatigue in there as well so we will give him a breather. "Almunia needs games so he will play, but Wojciech is all right and will be on the bench. "Diaby was not in the squad on Sunday. I was cautious with him. "He has missed many games this season and I did not want to take a gamble with the intensity of a cup final. He will play tomorrow night." Theo Walcott, who had already been ruled out against Barcelona, remains a fortnight away from recovering from his sprained ankle. "He is out. We said from the day he got the injury against Stoke you could count three weeks," said Wenger.
