Thomas Vermaelen joins Barcelona, Wenger cashes out wisely.

Thomas Vermaelen has swapped London for Barcelona

Alex Johnson is impressed that Arsene Wenger has secured 15million for his backup centre-back.

Arsenal captain Thomas Vermaelen has joined Barcelona after agreeing personal terms.

A 15m fee has been agreed and it comes as no surprise with Gunners boss Arsene Wenger doing little this week to dispel rumours the Belgian centre back would be moving on.

In ordinary circumstances, the loss of his skipper on the eve of the new season would be a stinging blow for Wenger.

This move however almost seems like it is being treated with derision by most observers.

It is far removed from the furore that surrounded Cesc Fabregas before he eventually made the same switch back in 2011 - a transfer followed up the next summer with subsequent skipper Robin van Persie departing for Old Trafford.

Who are the winners and losers in this deal, and is it possible Wenger is completing a shrewd piece of business?

For Vermaelen the appeal is clear.

Relegated to third choice at Arsenal last season, he ended the season having made only 21 first-team appearances - reduced by almost 50% on the previous two campaigns.

Having been troubled by a series of injuries to the Belgian, Wenger favoured Per Mertesacker and Laurent Koscielny as his first-choice central defensive pairing.

That he is being allowed to leave now is a clear sign that the Arsenal boss was unwilling to make any assurances his captain could expect more first-team football in the coming campaign.

Barcelona may not be quite the juggernaut they were under Guardiola, but few players would resist the lure of the Catalan calling.

Securing 15m for an injury-prone defender that is no longer a first choice could in time look like a masterstroke from the Arsenal boss.

Vermaelen's value to Arsenal has been ever decreasing since he burst on the scene after joining from Ajax in 2009.

A no-nonsense centre back with a real eye for goal - he scored seven times in his first Premier League season - that would turn out to be the pinnacle of his stay in North London.

Replacing Robin van Persie as club captain two years ago, Vermaelen looked set for a distinguished Emirates career.

That Wenger has apparently done so little to dissuade his captain from leaving is perhaps the biggest clue.

The mooted rumour that Wenger offered Manchester United a player-swap deal involving Chris Smalling would be a damning indictment of Vermaelen's plight at Arsenal.

He may have been feeling a touch unloved in North London, but the new surroundings he will take up in Spain will represent the biggest challenge of his career to date.

Arsenal are seemingly a club on the rise, with their trophy-famine over and Wenger making waves in the transfer market this summer.

Barcelona meanwhile, by their own lofty standards find themselves in something of a trough.

They exited the Champions League earlier than at any stage in the previous six seasons, surrendered their LA Liga title to Atletico Madrid in stuttering fashion and lost the Copa Del Rey final to bitter rivals Real Madrid.

Luis Enrique has a stiff task on his hands to reinvigorate Barca.

As he takes up his employment in Catalunya, Vermaelen will find himself partially filling the void left by the iconic Carlos Puyol.

His influence was reduced in recent times, but this will be the first campaign Barca have started without their inspirational leader since 1999.

Vermaelen's most recent performances in an Arsenal shirt were uninspiring and he looks less than assured of a starting berth in Spain.

Gerard Pique and Javier Mascherano were the first-choice pairing last season, although that was under Gerardo Martino.

To play the Barcelona way, defenders are required to be part of the tiki-taka movement.

Dani Alves, Jordi Alba and Martin Montoya tussle for the full back berths.

Vermaelen will have to join the queue with fellow new boy Jeremy Mathieu, signed from Valencia this summer for a similar fee.

A La Liga veteran after five campaigns with Los Che, the Frenchman will present a willing challenge to Vermaelen as they vie for new boss Enrique's approval.

Wenger may have used his cash-out option at just the right time.