The Gunners defender will not be available until mid-October after suffering a stress fracture of his lower back, with a move for Ashley Williams to be stepped up again

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By Wayne Veysey Arsenal captain Thomas Vermaelen has been ruled out for three months with a back injury,can reveal.The Gunners defender will be out until mid-October after being diagnosed with a stress fracture of his lower back.Vermaelen pulled out of the Gunners' pre-season tour of Asia to have treatment at the club's London Colney headquarters after returning to training with a back problem. Arsene Wenger admitted on Sunday that the Belgian could miss the start of the season but claimed that he did not know for how long the club captain would be on the sidelines.However, scans have shown that the injury is worse than originally feared and Wenger has now learned that he will not have the centre-back available for the first two months of the new campaign.The Arsenal boss had already made a move to sign Ashley Williams and will now step up his pursuit of the Swansea defender.As revealed by Goal, Arsenal agreed terms with Williams in May but have been unable to nail down a fee for the player with the Swans.The two clubs are understood to have re-entered negotiations last week in an attempt to bridge the divide between Swansea's £12 million valuation and the Gunners' unwillingness to pay more than £8-10m.It is understood that Wenger's plan has always been to have four senior central defenders in his first-team squad next season. The departure of Sebastien Squillaci has opened up a place, with the Gunners boss keen to add Williams to his established trio of Laurent Koscielny, Per Mertesacker and Vermaelen. Barcelona and Bayern Munich have both made enquiries for Koscielny but Wenger does not want to listen to offers for the Frenchman, who finished last season in outstanding form.Despite Vermaelen losing his starting place in the final months of 2012-13, Wenger also wants to keep the Belgian, although it is by no means certain that he will remain the club captain.