Postiga has attracted the attention of Manchester United, Tottenham and Juventus due to his goalscoring exploits with the Uefa Cup winners.
The 20-year-old netted 12 goals in 23 appearances last term as Porto romped to the Portuguese title but missed the Uefa Cup final success over Celtic through suspension.
He has already earned full international honours with Portugal and is one of the most sought-after commodities in European football.
Spanish outfit Betis are aiming to usurp their rivals in the quest to land Postiga's signature by offering ‚é¼6 million (£4.3 million) for the marksman.
Porto are believed to be prepared to sell Postiga for the right price but Betis's proposed figure is unlikely to tempt the Portuguese champions into doing business.
Even if Betis persuade Porto to accept their offer, the Seville-based club may struggle to cajole Postiga into moving to Estadio Manuel Ruiz de Lopera.
Betis' prospects of European football next term are slim and with Porto entering the Champions League, Postiga may feel it will be more beneficial to remain in his homeland unless there is further interest.
