Dusan Vlahovic has been labelled a "coward" by Fiorentina ultras for joining fierce rivals Juventus.
The Serbia international completed a €70million switch between the Serie A sides on Friday, the day he turned 22.
Vlahovic had previously turned down the offer of a new contract with Fiorentina, forcing the club's hand somewhat as he had just 18 months to run on his existing deal.
After reportedly rejecting proposals from Premier League sides Arsenal, Tottenham and Newcastle United among others, Vlahovic instead opted for fellow Italian club Juventus.
Having also lost Federico Bernardeschi and Federico Chiesa to Juve in recent years, Vlahovic's choice of club did not go down well with Fiorentina's devoted supporters.
The Partizan Belgrade academy product's home is reported to have been under surveillance in the days leading up to the transfer, while some fans took to the streets to protest.
And in an open letter released on Saturday, fans representing the Curva Fiesole group took aim at Vlahovic, president Rocco Commisso and director Joe Barone.
"So it's the usual, another small man without b****, without honour and without respect who goes to a club with no identity or sense of belonging," the statement read.
"Another ownership that after expressing its love for the Viola people, does what all their predecessors did: sell our best players to our historic rivals.
"We're no longer surprised by anything and certainly won't tear our hair out having lost yet another buffoon."
Commisso recently criticised Juventus for their financial mismanagement, and the Fiorentina ultras felt he could have done more to block the move going through.
"We ask you president, what did they tell you to convince you to do such a thing?" the statement added. "You, who told a child you would not sell any more players to Juventus.
"Congratulate Barone. He must've been convincing to tell you who knows what to talk you into an operation that, yes, brought in money but made you lose face in front of an entire city and beyond.
"How is it possible that you decided to do deals with the ultimate evil of that system that until the other day you fought against?
"We thought, with pride, that we'd left behind the dark period of sales for profit and deals with those who shall not be named, only to go straight back into it.
"A city that had totally embraced your battles and would've continued to embrace you in future, but now feels abandoned and betrayed."
Vlahovic is the joint-top scorer in Serie A this season with 17 goals from 21 appearances – a tally only matched by Lazio's Ciro Immobile.
He has converted 28 big chances since the start of 2020-21, more than any other player in Serie A, while the 33 league goals scored in 2021 matched Cristiano Ronaldo's record for the most in the Italian top flight during a calendar year.
In a final dig at Vlahovic, the letter concluded: "We aren't prepared to watch our passion be trampled on, as your transfer market people don't seem to represent your way of approaching this adventure with us.
"Our final message is for the squad, who are what really matter right now. You've proved that you have guts, we are with you. More battles await us and hopefully we'll prompt some regrets for those who left in the night like a coward."