Coach Sinisa Mihajlovic said he expects to "give explanations" to AC Milan chief Silvio Berlusconi but said he "won't resign" after a 4-0 mauling by Napoli on Sunday prompted fans to stage protests at the San Siro.

"I'm sure I will get a phone call," from Berlusconi, Mihajlovic said Sunday after leaving media waiting nearly an hour after the game before appearing at the post-match conference.

"He will be asking for explanations, but I won't hide. I will give them to him."

Asked if he would consider resignation, Mihajlovic added: "I've never resigned from a job, and I never will."

Milan hosted Napoli looking to bounce back from last week's 1-0 defeat away to Genoa.

Instead, the Rossoneri were handed a football lesson that has underlined the gulf in class between their side and a Napoli team that is beginning to underline their scudetto potential.

After a shaky start under new coach Maurizio Sarri, Napoli have been banging in goals for fun, routing Lazio 5-0 two weeks ago and, after the blip of a scoreless home draw with Carpi, beating champions Juventus 2-1 in Naples.

On Sunday, it was Milan's turn to be humiliated.

Brazilian midfielder Allan pounced on 13 minutes to break the deadlock and although Milan limited the damage Napoli were unstoppable in a clinical second half.

Lorenzo Insigne staked his claim for a place in Italy's starting line for two final Euro 2016 qualifiers next week when he beat Milan 'keeper Diego Lopez with a fine free kick effort three minutes after the restart.

Insigne pounced again on 68 minutes when a moment of hesitation among Milan's defenders allowed the diminutive striker to pounce from a tight angle and beat Lopez at the 'keeper's far post.

Milan's nightmare was completed when defender Rodrigo Ely, who had come closest for the hosts with a header from a free kick at the death, turned Faouzi Ghoulam's drive into his own net.

The own goal prompted fans to start leaving the stadium in droves and after the final whistle fans hurled abuse, shouting "Vergogna (Shame on you)" and "Andate a lavorare (Get to work)" at the players as they left the pitch.

It was Napoli's biggest ever win against Milan at the San Siro, but Mihajlovic refused to gloss over his side's defiencies.

"What can I say? They were a lot stronger than us," said the Serbian, who took over Milan following a solid season at the helm of Sampdoria last season.

"We gifted them the first goal and after the second went in the game was over. When you make individual errors like we did, players of Napoli's calibre make you pay."

Having seen Clarence Seedorf and Filippo Inzaghi fail to turn the Rossoneri's fortunes around, Milan fans are already getting frustrated seven games into the season. Milan sit in 11th place, nine points behind leaders Fiorentina.

The fact Mihajlovic once played for city rivals Inter Milan is also now bubbling to the surface.

One post on Twitter referred to a statement made by Mihajlovic prior to becoming Milan coach, when he said: "I will never coach Milan." The user (@FBiasin) said: "In the end, Mihajlovic is keeping his promise."

But the Serbian says Milan's struggles are not just physical.

"We're weak mentally," said Mihajlovic. "We work hard in training during the week, but obviously it's not enough.

"There's nothing else for it but to knuckle down and try to get out of this out as soon as possible."