Lord Coe has been accused of misleading a parliamentary doping inquiry in an explosive report by the Digital, Culture, Media and Sport select committee.
The 52-page document, the product of an investigation that lasted two and a half years, criticises some of the biggest names in British sport, including Sir Dave Brailsford and Sir Bradley Wiggins from cycling.
But its assessment of Coe's appearance before the committee in December 2015, and subsequent written response, is particularly scathing.
One of Britain's most famous athletes, Coe is now president of the International Association of Athletics Federations (IAAF), a body he joined in 2007 as a vice-president before taking the top job in 2014.
The committee's criticism is based on what Coe knew about his sport's problems with doping before they were revealed by investigative journalists and whistle-blowers from late 2014.
The MPs acknowledge the efforts he has made to restore the sport's reputation and protect clean athletes since late 2015 but make it clear they believe he should have done something about it much sooner.
The committee, chaired by Conservative MP Damian Collins, is also unconvinced by his claim he knew nothing of the role played by his predecessor, Lamine Diack, until the Senegalese administrator was arrested in November 2015.
The report said when Coe appeared before them he "sought to distance himself from knowledge of the allegations of doping", most notably in Russia, until they were exposed by a German documentary in December 2014.
This is despite former British distance runner and London Marathon director Dave Bedford phoning him in August 2014 to tell him about senior IAAF officials planning to hush up a Russian doping case in return for large sums of money.
Bedford followed up this call with an email to Coe containing attachments that outlined the plot. The existence of this email emerged six months after Coe's appearance before the committee but he declined its invite to return and explain in person.
Instead, Coe wrote to them and said Bedford had not discussed the details with him on the phone and he forwarded the email to the IAAF's ethics chief Michael Beloff QC, without opening the attachments.
The report describes Coe's answers on the issues of Russia's doping and the IAAF's complicity as "misleading".
It said: "Lord Coe may not have read the email and attachments, but it stretches credibility to believe that he was not aware of the main allegations that the ethics commission had been asked to investigate.
"It is disappointing that Lord Coe did not take the opportunity to make sure he was fully informed of the serious issues. These are matters of the greatest seriousness and affect the reputation of the IAAF and Lord Coe."
Collins was asked to expand on why the committee felt Coe had misled them and he said it was based on the attempt to "downplay" what he knew of the sport's precarious position.
But Collins said there is a "broader point to Coe's answers not being good enough" and that is the impression the IAAF gives of being "defensive" when evidence of doping is presented.
Coe has been asked for a response and in a statement, the IAAF said it would be writing to the panel "to explain some of the more complex aspects of anti-doping that have been misunderstood".