Chelsea are understood to have made a giant offer to lure Pato to Stamford Bridge.
However, AC Milan vice-president Adriano Galliani believes Chelsea would be wasting their time.
Galliani said: "We previously received a superior offer and we already said no to that, so the answer would be no."
Milan are keen to keep Pato at the San Siro having sold Kaka to Real Madrid this month.
Pato finished as Milan's second top scorer behind his Kaka in Serie A, with 15 goals in 36 league appearances last season.
He is under contract with the Rossoneri until June 2012.
Meanwhile, Chelsea target Maicon plans to remain at the San Siro – as long as he is given an improved contract.
The 27-year-old, who was a key figure as Jose Mourinho's Inter clinched a fourth straight Serie A title last term, has been linked with Chelsea this summer.
However, he insists he is settled in Italy and believes his demands will be met by Inter.
"As I have mentioned many times, I want to remain at Inter," said Maicon, who won the Confederations Cup with Brazil in South Africa.
"I am happy to play at Inter. We can reach an agreement without any problems.
"If they (Inter) have watched my performances in the Confederations Cup and want to recognise what I've done (with an improved contract), I will happily remain at Inter."