Mr Miliband described the reported claims as a "wrecking tactic" and added: "I hope people understand it for what it is.”
Mr Corbyn and an array of former shadow ministers from his time as leader made a submission to an internal Labour inquiry saying there is “overwhelming evidence” of sabotage from certain staff members in the party's headquarters, it was reported last week.
The submission, first reported on by the Guardian, endorses claims made in a Labour Party report leaked in April and reportedly suggests that it is not impossible that Mr Corbyn might now be in his third year as prime minister “were it not for the unauthorised, unilateral action taken by a handful of senior party officials”.
The 2017 election was narrowly contested and resulted in a hung parliament, with the Conservative Party - led at the time by then Prime Minister Theresa May - winning 318 seats in comparison to Labour’s 262.
But Mr Miliband - whose brother Ed is a former Labour leader and currently serves as the party's shadow business secretary under now leader Sir Keir Starmer - on Monday rubbished the reported claims, suggesting they were a "wrecking tactic from Jeremy Corbyn and the Corbynites".
"Denial after four successive defeats is a route to more defeats," he told Times Radio, citing Labour's last four general election performances.
"We learnt that after 1992, we got out of denial, and we won in 1997 and actually we won three elections on the trot."
He added: "When people got a look at Labour in 2017... we couldn’t beat the worst Tory campaign in history, 750,000 votes we were behind.
"And then when people got the full measure of Jeremy Corbyn in 2019 he led us to the worst election defeat since the 1930s.
“So it’s a wrecking tactic and I hope people understand it for what it is.”
The submission made by Mr Corbyn, former shadow chancellor John McDonnell and seven other former shadow ministers and aides reportedly argues that the senior Labour officials, who are not named, were uncooperative and refused to allocate resources to winnable target seats.
The dossier is said to be strongly opposed by the officials involved, one of whom allegedly called it “a mythical ‘stab in the back’ conspiracy theory to absolve themselves”, according to The Guardian.
Mr Corbyn’s claims, which the newspaper reported to have seen, were made jointly with Labour’s 2017 election committee which includes Mr McDonnell, the former shadow ministers Jon Trickett and Ian Lavery, and five senior aides to Mr Corbyn at the time: Karie Murphy, Seumas Milne, Andrew Fisher, Andrew Murray and Steve Howell.
It is reported the joint submission states the group “believe that there is clear evidence of factional activity by senior paid employees of the party against the elected leadership of the time”.
They allege that in 2017, officials hostile towards Mr Corbyn set up a shadow operation in Westminster to plot their own election course which included refusing to give potential target seats money and focusing funds on MPs not allied to the former Labour leader.
The submission reportedly argues that if the claims of money being spent in this manner without authority are correct, then it may have constituted fraudulent activity.