Marcelino has said he is "absolutely certain" that winning the Copa del Rey last season triggered his sacking as Valencia coach this week.
The Spaniard, who spent two campaigns at the helm of Los Che, was dismissed on Wednesday despite winning the Copa del Rey and securing Champions League football last season.
Speaking for the first time since being dismissed, Marcelino told a news conference: "I'm absolutely certain that what triggered this [sacking] was the Copa. During the season, we received direct messages from certain people that we had to reject the Copa [in order to concentrate on La Liga].
"But the fans wanted to fight for it. The players too and so did the coaching staff. Who would have told me that this would trigger this situation?"
Valencia beat La Liga champions Barcelona 2-1 in Seville on May 26 to lift the Copa while they finished fourth in La Liga despite a slow start to the 2018-19 campaign.
"We never received any congratulatory messages from the club owner [Peter Lim] after winning the Copa," Marcelino said.
"When I went to Singapore on July 19, he [Lim] only congratulated me for the Champions League qualification and not for the Copa. You can imagine my surprise."
Marcelino reportedly had a tense relationship with Lim over differences regarding Valencia's summer transfer policy.
However, the former Villarreal coach said he is still upset over the club's decision to dismiss him and appoint Albert Celades as his replacement.
"I was incredulous when they notified me," the 54-year-old said. "I felt helpless.
"I never saw myself out and it came as a surprise. When I met with the club owner on July 19 he told me face-to-face that he had absolute confidence in our work.
"After those comments, how could I think that I would be sacked on Sept. 10? I'm sad but thankful for the messages of support that I've received. I take with me the affection and respect from the players and those that worked with me here. Now I will take some time off."
Valencia, under new coach Celades, play at Barcelona on Saturday before beginning their Champions League campaign away to Chelsea next week.