Arsène Wenger called it his club's worst night in European competition, a 4-0 defeat devised and concluded by a player he might once have signed. Now Zlatan Ibrahimovic came back to haunt the north London club, dismantling Wenger's defence time and again before finishing them off from the penalty spot.

This was a display that underlined the painful truth of the 17 points separating Wenger's team from the Premier League leaders and revealed how much work remains to be done before claims of a revival can be made with any confidence. Against opponents as experienced as Milan they have only an infinitesimal chance of redeeming themselves at the Emirates Stadium in a fortnight and making further progress in this season's Champions League.

It is a virtual certainty, then, that they will be playing in Europe's top competition next season only if they succeed in finishing in the top four of the league. Based on the way they played last night, any assessment of that prospect would have to be deeply pessimistic. The financial consequences would be grave and criticism of Wenger's recent record – muted by signs of recovery in the past couple of weeks – would become more strident.

After inspecting the San Siro pitch, with its strips of recently relaid turf down both flanks, Wenger criticised the surface on the eve of the match. He returned to the subject in the aftermath of defeat, but from a different perspective. "It wouldn't be fair for me to blame the pitch, even if it was disastrous," he said. "Our performance was the same level as the pitch."

Milan's players could be seen replacing divots even during the warm-up but they adapted far more convincingly to the conditions – and one man in particular did so. A dozen years ago Wenger showed an interest in a gawky teenage striker who travelled from Sweden to London to meet the Arsenal manager but was unimpressed by the Frenchman's request to take part in a trial. When Ibrahimovic eventually left Malmo, it was for Ajax. Two years ago he returned to score twice for Barcelona at the Emirates and on Wednesday night, wearing the red and black stripes of Milan, he redoubled the pain despite scoring only once.

Never again will English critics be entitled to cast aspersions on Ibrahimovic's ability to perform on a big occasion. Ineffective as he may have been in November's friendly against Fabio Capello's side at Wembley, on Wednesday night he teased Arsenal to distraction. Had his team-mates capitalised on even half his promptings, the margin of victory would have been doubled.

Arsenal's supporters would have been glimpsing hope in the sight of a team sheet containing a recognisable line-up of defenders but it took only a quarter of an hour for Milan to puncture their optimism. Kevin-Prince Boateng located a fissure between the centre-backs and sent a powerful volley dipping under the crossbar.

Until then Arsenal's rearguard had just about coped with the task of smothering Milan's deliberate approach play, even when their own team-mates played them into danger. Although travelling to Milan still beset by the absence of important players, Wenger was able to field his first-choice back four for the first time in six months. Bacary Sagna, Laurent Koscielny, Thomas Vermaelen and Kieran Gibbs started the opening match of the Premier League campaign, at Newcastle United, and were reassembled for the Champions League play-off tie against Udinese at home on 12 August, keeping clean sheets on both occasions. Until last night that was the sum total of their contribution to the season as a unit but their reunion was not to be a happy one.

They may have been encouraged by the sight of Clarence Seedorf disappearing down the tunnel after only 12 minutes with what appeared to be a muscle strain. Uniquely distinguished as a four-times winner of the European Cup with three different clubs, the 35-year-old began the match in his customary unruffled fashion, easing himself into relevant positions as he established a rhythm for his colleagues. His departure, it seemed, could only be good news. Any such comfort, however, proved illusory. First came Milan's opening goal, followed in the 38th minute by another blow. Ibrahimovic drifted lazily past Sagna down the left and rolled the ball casually with his studs before clipping in a centre from the byline that Robinho headed past Wojciech Szczesny with as much effort as he might have expended on lighting a cigarette.

It was 20 years ago that Vanessa Redgrave, taken by her Italian ex-husband to see Milan beat Gothenburg 4-0 with Marco van Basten scoring all four, likened a big European occasion at San Siro to a first night at La Scala. The stadium had not exactly been rocking as the match began, an attendance of 64,000 leaving large tracts of empty seating in the stalls and upper circle, suggesting either the effects of a 30% unemployment rate among young Italians or a certain blasé attitude among the supporters of a club whose seven victories put them second only to Real Madrid's nine. But the tangible evidence of Milan's superiority over the representatives of English football as defined by the second-half goals for Robinho and Ibrahimovic got the songs going and the flags waving, with the Arsenal contingent reduced to silent contemplation of an uncertain future.