Cesare Prandelli claims Valencia went back on their promise to reinforce the squad in January and has accused the club of being run by "numbers people" after walking away from Mestalla.
The Italian coach abruptly quit after three months in charge on Friday, leaving the team 17th in LaLiga and facing a desperate struggle to avoid the drop.
Senior club officials, speaking at a news conference on Saturday, accused the former Italy boss of "giving up and abandoning ship", only for Prandelli to hit back in his own media briefing shortly afterwards.
"I was promised that we were going to buy footballers," he said.
"I spoke with [Simone] Zaza's father and he told me that he was very happy to come [to Valencia]," Prandelli said of the Italy international forward, who is on loan at West Ham from Juventus but likely to leave London Stadium in January.
"I spoke with [sporting director Jesus Garcia Pitarch] Suso so that they would meet immediately to finish the Zaza [signing]. [We] needed a player with character.
"I was told that the four-player [recruitment] project was reduced to one player."
While Prandelli has incurred the displeasure of owner Peter Lim and his representatives at the club, the former Fiorentina coach, who follows Gary Neville and Pako Ayestaran in making a swift exit, is adamant he gave the role his best effort.
"It is difficult ... when dreams end," he said.
"We have tried everything but we have reached today.
"I make this appearance because I feel a great respect for the city of Valencia and the fans of Valencia.
"I'm going with my head held high, having tried everything possible.
"This club is run by numbers people, but football is more than numbers.
"[For] Valencia, I ask the fans to help from this very Tuesday," he added, referring to the first leg of the Copa del Rey round-of-16 tie at home to Celta Vigo.