The Brazilian said team boss Flavio Briatore, who is believed to have told Piquet in Budapest last weekend that he has been ousted in favor of reserve Romain Grosjean, only cares about profits and "doesn't understand shit about F1".
"He is my manager. But in his role of team boss he doesn't respect me," Piquet told the Italian magazine Autosprint.
"He only thinks about money, about how much money he can pocket in everything he's involved with. He's a man with no friends."
The outburst followed Briatore's claim that Piquet had "opened the booked of excuses" to explain his struggle to get up to speed in F1 since making his debut early last year.
"When a driver lacks results, he opens the book of excuses and begins, 'the fault is the weather, a spectator's sunglasses, a spin on the straight, this and that'," Briatore said.
"It's not true that there's a technical difference of seven tenths between Alonso's and Piquet's car.
"If that was true, we'd have a car capable of winning the title. And that unfortunately isn't the case," he added.