Flynn has declined to testify to the US Senate Intelligence Committee about his Russian ties, invoking his constitutional right to avoid self-incrimination.
The issue will be front and centre this week in Washington, where former FBI Director James Comey is due to testify on whether Trump tried to get him to back off an investigation into alleged ties between Trump's election campaign and Moscow.
The decision was reported by the New York Times, which attributed information about the decision to unnamed senior officials with the Trump administration.
A second White House official confirmed that the issue is under review. Warner added, "I want to know what kind of pressure, appropriate or inappropriate, how many conversations he had with the president about this topic".
"You don't do that, I think, by invoking executive privilege on a conversation you had apparently with nobody else in the room", the Missouri Republican said.
"Those who don't know the first thing about the law immediately began hurling words like "obstruction of justice", "high crimes and misdemeanors" and "impeachment", Gregg Jarrett, a former defense attorney who now works as a Fox News Anchor, wrote at the time in a piece entitled "Comey's revenge is a gun without powder". However, a memo written by Comey suggested that the president asked him to end its investigation into Michael Flynn.
"When Director Comey goes to testify, I think that will be a very clarifying moment", she said.
Senators will nearly certainly ask Comey whether Trump asked him to drop an Federal Bureau of Investigation probe into Flynn's contacts with Russian government officials.
WASHINGTON (CNN) - Former FBI Director James Comey was "disturbed" by his interactions with President Donald Trump but "he thought he had the situation under control", a source familiar with Comey's thinking tells CNN. Specifically, given how massively politically disadvantageous it would be ― sending a clear message, whether accurately or not, that there's something to be feared in Comey's testimony ― to try to throw up roadblocks anyway would suggest something dire about whatever the administration is anxious about.
The White House has rebuffed questions about whether Trump was suggesting he had recorded his discussions with the former Federal Bureau of Investigation chief.
Had Trump kept silent, "He would have had a stronger basis because of the ongoing Russian Federation investigation", Rozell added.
The initial decision to fire Comey presented similar concerns and pitfalls for the administration as the current decision whether or not to try to halt his testimony does. The memo was filed on February 14 following an Oval Office meeting with Trump and a day after Trump fired Flynn for misleading Vice President Mike Pence about his contacts with Russia's ambassador.
White House spokesman Sean Spicer told reporters Friday he was unaware if the president would try to block Comey's testimony.
The requests involved between 30 and 40 top-secret reports on intercepted communications in which foreign officials outside the United States mentioned the Trump campaign and people involved in it, the officials said.