Mhairi Black, who represents Paisley and Renfrewshire South at Westminster, said she felt “let down” by the Labour leader, claiming he had “sold his soul over independence”.
In an interview with the Huffington Post, Ms Black said that by “talking to him (Corbyn)” she knew he did not accept Labour’s policy of supporting the Union between Scotland and the rest of the UK.
She did not reveal where or when the conversation with Mr Corbyn took place.
A Labour party spokesman said the claims were “complete nonsense.”
Senior sources close to Mr Corbyn accused the Nationalist of lying over the claims. “This is categorically untrue,” they told the Red Robin, a pro-Labour blog. “It just didn’t happen. It is a desperate lie and untruth”.
Ms Black said in the interview: “I’m raging at Jeremy. He has totally sold his soul, especially in terms of Scotland.”
She continued: “It really annoys me when people get credit when the reality is different.
“I was excited by Jeremy Corbyn for the same reason as all the Labour membership were, but since he has got into that position of power, what’s he done?
“He has had unelected lords in his cabinet. He’s had scandal upon scandal, and don’t get me wrong, I get that there is a whole lot of backbenchers against Jeremy, but he has sold his soul.
“He has sold out in terms of austerity. He has sold out in terms of Scottish independence – because I know that he doesn’t believe the things he says about independence now.”
Asked directly by the website as to how she knew Corbyn supported independence, she said: “From talking to him.”
Mr Corbyn has previously said he was against Scottish independence as it would be “catastrophic” for those living there by causing “turbo-charged austerity”.
But some in his party have questioned his commitment to the Union.
One Scottish Labour source told The Scotsman: “I find it hard to be believe he would be naive enough to say so to Mhairi Black, but is it plausible? Of course it is.
“He didn’t lift a finger during the independence referendum campaign. He’s surrounded by people who hold those sorts of views.
“The problem isn’t so much whether it’s true or not - it’s that Scottish voters already don’t trust Jeremy Corbyn to protect the Union.”
Scottish Conservative constitution spokesman Adam Tomkins said: “This is yet more confirmation that Labour isn’t just soft on the independence issue, it doesn’t even care.
“From Jeremy Corbyn to Kezia Dugdale, it’s clear the party is willing to sell out the two million people who voted No in 2014.
“Labour leaders on both side of the border paid unconvincing lip service to the importance of the union, yet behind the scenes would vote Yes in a heartbeat.”