Fox Sports has sacked Jamie Horowitz, head of sports programming at the US company.
It gave no reasons for the dismissal, but stressed on the importance of "professional conduct".
Meanwhile, US media report that Mr Horowitz's departure comes amid claims of sexual harassment at Fox Sports.
Mr Horowitz's lawyer said "the way Jamie has been treated by Fox is appalling" and that the executive had worked "in an exemplary fashion".
In the memo to sent to employees, Fox Sports President Eric Shanks wrote that everyone "should act with respect and adhere to professional conduct at all times".
"These values are non-negotiable."
Mr Horowitz's lawyer Patricia Glaser said in response to his dismissal: "At no point in his tenure was there any mention by his superiors or human resources of any misconduct, nor an inability to adhere to professional conduct.
"Jamie was hired by Fox to do a job, the job that until today he has performed in an exemplary fashion. Any slanderous accusations to the contrary will be vigorously defended."
However, Fox Sport's lawyer Daniel Petrocelli said that "Mr Horowitz's termination was fully warranted and his lawyer's accusations are ill-informed and misguided."
Fox Sports is part of 21st Century Fox, which is owned by Rupert Murdoch.
The Los Angeles Times and the New York Times reported that about a week ago Fox began an investigation into claims of sexual harassment at its sports division. The newspapers quoted a person briefed on the matter.
Fox has not publicly commented on the media reports, which could not be independently verified.
In April, prime-time presenter Bill O'Reilly was dropped from Fox News over sexual harassment claims. He described the claims as "completely unfounded".
Last July, Roger Ailes, a long-time boss of Fox News, resigned after a number of female employees had accused him of sexual harassment.
At the time he said he was resigning because he had become a "distraction". Mr Ailes died in May.