The daily, citing two people familiar with the case, said Flynn told the presidential transition team's chief lawyer Don McGahn about the investigation on January 4 -- weeks before assuming the highly sensitive post.
Flynn, who ended up being fired from the position after just 24 days, is at the center of a sprawling federal investigation into alleged Russian interference in the 2016 US presidential election.
The White House has said that Flynn was dismissed for misleading Vice President Mike Pence about a phone call with the Russian ambassador, during which he reportedly discussed ways of softening US sanctions on Russia.
Trump repeatedly tried, without success, to get FBI director James Comey to drop the probe into Flynn.
A decorated retired general, Flynn during the Barack Obama adminstration was ousted as the head of the Defense Intelligence Agency.
Obama, shortly after last November's presidential election, reportedly warned Trump not to hire Flynn for the national security post, according to news reports -- advice the billionaire businessman failed to heed.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)