The former prime minister faces a crucial televised evidence session in front of the Commons Privileges Committee on Wednesday.
The committee is yet to publish its final verdict - but its initial update earlier this month said Mr Johnson may have misled Parliament multiple times.
Mr Johnson denies misleading MPs.
Wednesday's session, which could last up to five hours, will be a key chance for Mr Johnson to persuade the seven cross-party MPs who make up the committee that he did not mislead MPs in December 2021 - including when he told the Commons that he had "been repeatedly assured since these allegations emerged that there was no party and that no Covid rules were broken".
In May last year, an inquiry by senior civil servant Sue Gray found widespread rule-breaking had taken place, and Mr Johnson was among 83 people fined by police for attending law-breaking events.
If he fails to convince the committee and is found guilty, he could be suspended from the Commons, and even faces a recall petition, which would trigger a by-election, if that suspension is for more than 10 days.
Crucially, though, MPs would have to approve any sanction on Mr Johnson.
Sources close to Mr Johnson claim he will publish a "compelling dossier" that will provide evidence and arguments that he did not knowingly mislead parliament.
The Sunday Times, Observer and Sunday Telegraph also report that his "dossier" will include advice he claims he was given at the time by No10 aides, advising him that Covid rules were not broken.
The Sunday Times quotes one source saying the messages show "in black and white" that what Mr Johnson told Parliament was what he had been advised to say by officials and his No10 team, claiming he was forced to rely on advice because he was not at some of the events.
The newspapers also report that his defence may repeat allegations of bias levelled at the former top civil servant Sue Gray, whose inquiry found widespread rule-breaking had taken place in Whitehall during Covid.
Sue Gray has since resigned and has been offered a job as Sir Keir Starmer's chief of staff, which caused anger among allies of Boris Johnson including his former cabinet colleagues Jacob Rees-Mogg MP and Nadine Dorries MP.
The Labour Party has said it will give all the information related to its approach to her to the Advisory Committee on Business Appointments (ACOBA) - the government's appointments watchdog.
But minister Jeremy Quin has said her proposed move may have breached Whitehall's rules, as approval must be obtained prior to a job offer being announced.
Downing Street sources say any sanctions against Mr Johnson would be a matter for the House of Commons and MPs will therefore be given a free vote - meaning they will not be "whipped" to vote a certain way.
That means Tory MPs would not be asked to vote one way or another, as they were over the proposed suspension of Owen Paterson in November 2021, when Mr Johnson was still prime minister.
The government tried to block Mr Paterson's suspension from the Commons but, after a backlash, was later forced to U-turn. He then resigned as an MP.
At the time, Mr Johnson came in for criticism from many of his own MPs about being told to back Mr Paterson, amid Labour accusations of "sleaze". The first Partygate stories broke only a few weeks later.
The Paterson row was the beginning of the end for Mr Johnson's time as prime minister, and Mr Johnson later admitted he "crashed the car" in his handling of the case.
A spokesman for Mr Johnson said: "The Privileges Committee will vindicate Boris Johnson's position.
"The evidence will show that Boris Johnson did not knowingly mislead parliament."
The seven cross-party MPs on the Privileges Committee are investigating whether Mr Johnson misled Parliament over gatherings at Downing Street during Covid lockdowns.
In interim findings earlier this month, the committee suggested Mr Johnson may have misled Parliament multiple times over, saying it had seen evidence that "strongly suggests" Covid rule breaches would have been "obvious" to Mr Johnson.