Gen. Michael Flynn, former national security adviser to US President Donald Trump, leaves Federal Court December 1, 2017 in Washington, DC.

President Donald Trump's lawyers in the Russia investigation want to undermine the credibility of ex-national security advisor Michael Flynn if he alleges wrongdoing by top White House officials, The Washington Post reported, citing three sources.

Flynn, , is reportedly cooperating with special counsel Robert Mueller. Mueller is investigating Russian efforts to influence the 2016 election and possible collusion between the Trump campaign and the Kremlin.

The president's outside counsel John Dowd denied the report.

"Complete nonsense! More fake news," Dowd told NBC News.

If Flynn moves to accuse Trump or top aides of wrongdoing, the president's legal team plans to describe him as a liar who wants to shield himself, the Post reported.

Trump has repeatedly defended Flynn's character in the past.