Arsenal's William Gallas is a doubt for Porto Champions League tie

William Gallas faces a race to be fit for next Tuesday's Champions League match against Porto, after he was ruled out of Saturday's Premier League fixture with Burnley. Arsenal's key central defender has struggled for some weeks with a problem which stems from his lower back and is currently affecting his calf. He has not played since the Premier League victory over Liverpool on 10 February and was missed in the first leg of the Champions League last-16 tie against Porto in Portugal, which Arsenal lost 2-1. Arsène Wenger, the manager, is desperate for Gallas to take his place for the second leg, as his partnership with Thomas Vermaelen has been impressive this season. Gallas's back-up is Sol Campbell but he was partly culpable for Porto's second goal and he, too, is struggling with a problem, to his groin. With Johan Djourou a long-term knee injury casualty, Wenger's other option in central defence is Mikaël Silvestre. "Gallas is still out," said Wenger, "and we have a little problem with Campbell. We will check on that before the Burnley game." Wenger revealed at the end of January that Gallas had been pressed through the pain of his muscular injury on a number of occasions and he had been fortunate to escape serious injury. Yet, as the season enters its final stretch, there clearly remains a concern, despite him playing some part in training over the course of this past week. Wenger could report more encouraging news further forward in his team. With Aaron Ramsey out for eight months with his double leg break and Alex Song suspended for two matches, he could be grateful that Denílson and Andrey Arshavin have regained fitness following calf and hamstring problems respectively. Abou Diaby, meanwhile, is close to a return from his calf injury. "We have the luck that Denílson could be available again," Wenger said. "He did not travel to Stoke last week because he had an injury to his calf. Arshavin could be available and there is a little, little chance that Diaby could be available again, too. "I am convinced that Denílson and Arshavin will be OK but for Diaby it is 50-50." Carlos Vela, Wenger added, would not play against Burnley following his midweek international exertions for Mexico.