Paul Manafort is going to jail for witness tampering tomorrow, according to one former US attorney.

Harry Litman, who now lectures at the UCLA School of Law, advised Trump's former campaign manager to 'bring his toothbrush' when he appears in court on Friday

'I think he's going to jail. This is the stupidest thing a suspect can do, this kind of witness tampering' Litman told MSNBC.

Paul Manafort has been advised to 'bring his toothbrush to court' on Friday by one former US attorney who says he 'is going to jail' for witness tampering

Manafort's only hope of avoiding the inside of a cell 'is to somehow try to construe [the tampering] in a way that makes it different to what it was,' Litman said.

But he also described Manafort's attempts as 'ham handed' and 'blatant'.

'The statute says, if they find this happened, there’s a presumption that no circumstances exist that will' excuse him, Litman added.

Manafort was already facing charges of money laundering and tax fraud uncovered by Robert Mueller as he probes Russian interference in the 2016 election.

The charges related to millions of dollars that Manafort was given while lobbying on behalf of the Russian-backed regime in Ukraine before it was toppled.

Harry Litman, who now lectures at the UCLA School of Law, said the statute around witness tampering means there are 'no circumstances' that will excuse Manafort if he is found guilty

Earlier this week Mueller said that his team had uncovered encrypted messages which showed the 69-year-old had been in contact with witnesses in his case.

The messages were an 'effort to influence [witness] testimony and to otherwise conceal evidence', the FBI says.

Manafort was found to be in breach of his bail and summoned back to court.

Donald Trump has repeatedly described the FBI investigation as a 'witch hunt' and said no evidence of collusion has been found.

That is despite the fact that four men associated with his campaign, including his one-time National Security Adviser Mike Flynn, have been indicted.