Special counsel Robert Mueller (2nd L) leaves after a closed meeting with members of the Senate Judiciary Committee June 21, 2017 at the Capitol in Washington, DC.

Special counsel Robert Mueller's investigators met last year with a pollster who worked on Donald Trump's 2016 presidential campaign and is a former associate of Trump's ex-campaign chief, Paul Manafort, according to a new report.

The report from CNN adds more intrigue to the recent revelation that Manafort himself was accused by Mueller of sharing polling data with Konstantin Kilimnik, whom Mueller has alleged holds "ties to a Russian intelligence service," during the 2016 election.

Mueller has been investigating Russia's meddling in that election, as well as possible coordination between the Kremlin and Trump campaign-related figures. Some Democrats and pundits see Manafort's distribution of the polling data as new evidence of possible collusion.

Trump has long denied any wrongdoing during the campaign and has labeled Mueller's probe a "phony witch hunt."

Asked Thursday about the allegation against Manafort — which was intended to be hidden from the public within a court filing from the former campaign chief's lawyers — Trump said he "didn't know anything about it."

CNN reported that Tony Fabrizio, a partner at Republican public opinion firm Fabrizio, Lee & Associates, was spotted leaving the special counsel's office on Feb. 1, 2018, and has since been confirmed to be meeting with investigators at that time.

Fabrizio's firm did not immediately respond to CNBC's request for comment on CNN's report. A spokesman for the special counsel declined to comment.

A source familiar with the Russia probe told CNN that Fabrizio was questioned about past polling work for elections Manafort worked on in Ukraine. Manafort pleaded guilty in September to conspiracy charges related to that Ukraine work, and had agreed to cooperate truthfully with Mueller's team.

Read CNN's full report on Fabrizio's meeting with Mueller's team.