Pallotta told his club's official website that he was surprised Monchi, full name Ramon Rodriguez Verdejo, told reporters in Spain he left Roma because "the president (Pallotta) wanted to go right; I wanted to go left" after returning to Sevilla less than two years after arriving in Rome, snubbing an offer from Premier League club Arsenal.
"I want to make something very clear; right from the start, I was very clear about the direction I wanted us to go in and that’s why we spent a lot of money bringing Monchi in," Pallotta said.
"I gave him 100 percent control to appoint the coach he wanted, to employ the assistant coaches and the performance staff, to manage the scouting and to bring in the players he wanted. If you look at our results and our performances, it’s clear that this hasn’t worked."
Monchi, 50, left the stuttering capital club in the wake of coach Eusebio Di Francesco's sacking, which came after defeats to Porto and local rivals Lazio that left them out of the Champions League and struggling to qualify for the competition next season.
Roma are fifth in Serie A, four points behind AC Milan in the last Champions League place after losing 2-1 at struggling SPAL at the weekend.
It was the latest defeat of a disappointing season that has seen Roma fail to build on reaching the Champions League semi-finals last year after selling several key players in the summer, including now-Liverpool goalkeeper Allison.
"In November ... I asked Monchi for his Plan B should things continue to get worse. He had sole responsibility for football operations at Roma but he didn’t have a Plan B," said Pallotta.
"Please let me know what Monchi wanted to do differently? We gave him complete control and now we ... are in danger of missing out on finishing in the Top 3 for the first time since 2014."
Roma appointed Roman-born coach Claudio Ranieri to salvage a season that is close to going off the rails, but are yet to name a successor to Monchi.