The Edinburgh South MP, who is standing for the UK party deputy leadership, says Findlay used the term of abuse when the pair clashed during an argument over the constitution.
But Findlay, the Lothians MSP, took to social media today to reject the claims.
He tweeted: "It is pathetic that because @IanMurrayMP looks like he will be last in the Labour Deputy Leadership election he resorts to desperate slurs and made up stories about those he disagrees with - #spatthedummyout."
Murray told the Daily Record newspaper today that the last time he had contact with with Findlay, Jeremy's Corbyn's chief left-wing ally in Scotland, that the Lothians MSP used the C-word towards him. It came after Murray had challenged him on why he had "gone soft" on the constitution.
It's understood the contact happened some time ago by text message.
Murray has been a long-term critic of Jeremy Corbyn and recently accused the UK leadership of throwing Scottish Labour “under a bus” when Shadow Chancellor John McDonnell announced last year that a future Labour Government would not block a future vote on leaving the UK.
And he insisted that the focus on the independence issue in Scotland has been damaging for Labour.
“Over the last ten years, we’ve been swamped and paralysed, possibly even poisoned by the constitution,” he told the Record.