Kier Starmer refused to reveal when Sue Gray was first approached for a senior job with the Labour Party.
He was asked if he could prove a timeframe of when conversations first began with the high-profile Whitehall civil servant.
The Labour leader dodged directly answering during his visit to Ulster University in Northern Ireland.
Ms Gray headed up the bombshell report in May 2022 that investigated lockdown-busting parties in Boris Johnson's government.
Mr Johnson was forced out of government just weeks later.