Matt Gaetz could see charges brought against him by federal prosecutors in July, a report says.
Greenberg, a former Seminole County tax collector, pleaded guilty to a string of charges last month and has been cooperating with federal agents looking into Mr Gaetz.
Greenberg pleaded guilty in May to charges of stalking, identity theft, wire fraud, and conspiracy to bribe a public official, as well as a sex trafficking charge.
He is prepared to hand over evidence that could allegedly implicate Mr Gaetz and others, according to ABC News.
Sources told the US news organisation that the investigation into Mr Gaetz has picked up speed with agents interviewing more women who were allegedly introduced to the lawmaker by Greenberg.
Mr Gaetz has not been charged with any crime related to the case.
The pro-Trump politician has strongly denied any claims against him or participating in any illegal behaviour.
And a spokesperson for Mr Gaetz has previously described the investigation as a “partisan smear job.”
A new round of target letters and subpoenas in the wide-ranging investigation have been sent out since May, according to ABC News.
Greenberg will be sentenced by a federal judge on 19 August.
In his guilty plea Greenberg, a married father of two, admitted to spending more than $700,000 in 105 transaction to pay women for sex between 2016 and 2018.
He has acknowledged in court filings that one of those women was under 18 “for part of the time.”
The investigation targeting Mr Gaetz was launched last year when Donald Trump was still president, according to ABC News.
Then-Attorney General Bill Barr was briefed several times on its progress.