The collapsed transfer of Alvaro Pereira to Chelsea have been blamed on blues manager Andre Villas-Boas.
Reports point the finger squarely at the new Chelsea boss, who refused to meet Porto's £26.5 million asking price for the wing-back.
The player's agent Flavio Perchman says the issue lay with the Portugese chief and his own switch from the Europa League champions this summer.
When asked about the collapse of the deal, Perchman said: "Unfortunately, the operation fell apart and there was no way it could be rescued.
“Porto have broken their word. Last year they promised to sell Alvaro Pereira if they received a proposal worth more than £18m.
“Chelsea made such an offer, but they cut off the possibility of Alvaro going, even though he is a player who has given everything for Porto. They refused all proposals.
"I think that Porto have used Alvaro Pereira to take revenge on Chelsea over what happened with Villas-Boas."
Villas-Boas had been linked with a summer raid on his former club, with Pereira and star striker Falcao, who has subsequently joined Atletico Madrid, just two of the names mentioned in connection with the west London side.
Perchman admitted that his client is frustrated that the move failed to materialise and hinted that the wing-back could be on his way out of Porto at the next available opportunity.
“Chelsea were interested for many days. Porto began by setting a certain value but Chelsea always tried to get closer than they intended to Porto. But Porto never relented.
“The frustration for Alvaro is that he had a promise. After the year he had for the club, helping Porto to win all they won, letting him move to Chelsea would have been his reward.
“Let’s see what happens in the future. But he will not stay any longer than he has to. We will see how he reacts," he said.