Several European giants are thought to be in the market for the 24-year-old, with Manchester City, Chelsea and AC Milan among the teams to be linked.
However Hulk, who signed a five-year extension on his deal with treble-winning Porto in May, has a 100million euro (?89.5m) release clause.
The player has continually stressed his intention to remain at the Estadio do Dragao and his agent, Teodoro Fonseca, claims Porto snubbed the 80m euros offer without leaving room for any negotiation.
"I would be lying if I said no proposals have emerged to sign Hulk," Fonseca told Portuguese newspaper Record.
"I think the highest bid was 80million, but Porto did not even want to negotiate."
Fonseca refused to be drawn on which club had tried to lure Hulk away.
He added: "I cannot reveal that. But it is not hard to see because there are only three or four clubs who are able to present those kind of numbers for a player."
The appointment of former Porto boss Andre Villas-Boas as manager at Chelsea has fuelled speculation that Hulk is poised for a move to Stamford Bridge.
Source: Team Talk
Source: Team Talk