Lazio midfielder Keita Balde did not report for training on Wednesday because he is "exasperated" by the club, his agent has told La Gazzetta dello Sport, warning that they "could lose him for free."
Balde was left out of the squad for the Super Cup win over Juventus and did not appear at the Formello training ground on Wednesday as speculation about his future increased.
Agent Roberto Calenda said his client was unhappy with how he had been treated, adding: "He's exasperated by behaviour from the club which he is no longer willing to put up with.
"There have even been offensive comments written on the walls at Formello, clearly fuelling the misleading remarks with which Lazio are managing the whole issue."
Juventus have had a bid for 22-year-old Balde rejected, while Tottenham Hotspur, AC Milan and Inter Milan are reported to be monitoring the situation.
Calenda claimed Lazio were asking too much for the former Barcelona youth player, adding: "While president [Claudio] Lotito talks about selling him, he values Keita like a top player -- only when he offers him a new contract, he rates him like a normal player.
"Lazio continue to ask the Earth for a player who, in a few months, will be free to walk away for nothing.
"If they continue to pull on the string, then this is only going to snap and they are going to have to explain to their fans how they managed to lose a talented player like Keita for free."
Calenda said Keita had "earned recognition from the entire footballing world with his constant dedication and with the quality and efficiency of his play."
He added: "Now he's 22, which is the right age for a player to start to earn the first benefits of his talent and dedication.
"Despite the results, Lazio have never demonstrated that they believe in him and to have the project for him that he deserves."
He claimed the club had promised him "a contract worthy of a top player" and "a place in the team under [Simone] Inzaghi," adding: "But none of this has happened -- no new contract was offered, and he only started to play with a bit of regularity under Inzaghi towards the end of last season.
"Despite this, he paid them back with 16 goals. He continues to be earning far less than forwards who even played less than him in 2017."
Calenda added that it was "hard to have any kind of dialogue" with Lazio and said: "A while ago, I wrote to ask for a meeting, but I never even got a reply. It's a kind of relationship that I am not used to."
He claimed Keita's omission from the Super Cup squad had been "a really horrible sign for a player who has done what he has done for Lazio" and said: "He was really hurt and now the club are paying the consequences."