The decision was confirmed in a brief statement issued by the club on Sunday evening, hours after a 2-1 home defeat to Torino left Fiorentina without a point from their opening three fixtures of the season.
"ACF Fiorentina announces that Fabio Grosso has been relieved, effective today, of his role as head coach of the men's first team," the statement read.
Grosso's dismissal followed a disastrous start that began with a 4-0 defeat away to Roma, continued with a 3-0 home loss to promoted Frosinone on the day of the club's centenary celebrations, and was completed by Saturday's reverse against Torino, in which Fiorentina had led through a goal from Pellegrino before conceding twice.
Beyond the results themselves, performances had also drawn criticism, with the team appearing to lack ideas and a coherent attacking plan following a summer squad rebuild overseen by sporting director Fabio Paratici.
According to reports, the split stemmed at least in part from disagreements between Grosso and Paratici over the direction of the club's transfer business over the summer, with the two men said to have differed significantly on squad construction and the handling of new signings.
Those tensions came to a head following the Torino defeat, when club hierarchy resolved to make a change rather than persist with a project barely three months old.
Fiorentina moved quickly to identify Grosso's successor, settling on Paolo Vanoli, who had steered the club to safety last season after being brought in during November to replace the sacked Stefano Pioli, and went on to guide Fiorentina to the Conference League quarter-finals.
According to TMW, Vanoli is expected to sign a two-year contract, though it may be structured as one year with a further season as a club option. Thiago Motta had also been considered for the role but was ruled out before a final decision was made.
Vanoli, who had expressed disappointment at not being retained by the club over the summer, is due to be unveiled at the Viola Park on Monday afternoon and could take his first training session in charge that same day, ahead of Friday's match against Venezia. Grosso, a World Cup winner with Italy in 2006, arrived at Fiorentina this summer following a positive spell in charge of Sassuolo, but leaves after just three competitive matches in what proved to be a brief and turbulent tenure in Florence.