Soccer:Arsenal's need to sign a defender became even more urgent today after Arsene Wenger confirmed he could be without Thomas Vermaelen for another six weeks. Vermaelen's long-awaited comeback has once again been put on hold.

The Belgium star is due to undergo a small operation tomorrow in a bid to cure his troublesome Achilles injury. The 25-year-old, who has spent more than four months on the sidelines, will be out for another four weeks minimum, all but ruling him out of the first leg of the Gunners’ Champions League last-16 clash with Barcelona.

He could even miss the following month’s second leg if he requires the full six weeks to recover, with manager Wenger conceding the length of time the player has already been out meant he could not be rushed back. Vermaelen’s injury, picked up while he was on international duty in September, was originally expected to keep him out for a week.

But three failed comeback attempts have forced the player to go under the knife. With Sebastien Squillaci (hamstring) out until next month, Wenger has been left with Laurent Koscielny and Johan Djourou as his only recognised senior centre-backs and he admitted last week he needed to bring in cover before the end of the transfer window.

Bolton’s Gary Cahill has been linked with the north Londoners but he would not come cheap, while Wenger has dismissed any move for Sol Campbell. He said today of Vermaelen’s latest setback: “It is to take out a little ligament next to his tendon. It is to open it a little bit and cut out the ligament that has been causing the friction.

“It is a procedure — that is the right medical term. We are very optimistic (that this will cure the problem). But, of course, it is now what you call in football a little bit longer delay of four to six weeks.”

Wenger refused to rule Vermaelen out of next month’s Barcelona showdown but compared his injury to that of Aaron Ramsey, who has recently returned from a broken leg.

“Let’s count the weeks to Barcelona and you will know,” Wenger added. “I count a minimum of four weeks, maximum six, so it is not an unrealistic target. But don’t forget as well, he is a little bit in the situation of Aaron Ramsey, he has not played since the beginning of September. That means he will need some games to be completely fit.”