On a Monday television news show, Randy Evans rebutted claims that there is such a probe and elaborated Wednesday in an interview.
"There is no grand jury," Evans told Atlanta-based WXIA and the Savannah Morning News. "That's just not true."
Deal's opponents - first GOP primary foe Karen Handel and now Democrat Roy Barnes - have used talk of such a probe as a battering ram.
The speculation stems from claims then congressman Deal lobbied Georgia officials about his company's lucrative business arrangement with the state.
He denies any wrongdoing.
Evans said legal procedure calls for Deal's attorney - in this case Evans - to be notified if a grand jury has targeted him. That hasn't happened, Evans said.
Patrick Crosby, spokesman for the U.S. Attorney's office in Atlanta - where the investigation supposedly is based - said it's "standard practice" not to confirm or deny there is an investigation.
He also declined to say whether the attorney for a target of an investigation is supposed to be notified.
But James Durham, speaking for the U.S. Attorney's office in Savannah, said the office "usually will respond" if someone's lawyer asks if he's "a subject or a target" of grand jury scrutiny.
Barnes is airing TV ads claiming that - if elected - Deal could be distracted from his duties by a grand jury probe.
The former governor told The Associated Press Monday ethics questions surrounding Deal should disqualify him from being governor.
"There will be no September or October surprise," Evans said, rejecting hints by Barnes' campaign Deal might soon be indicted.
Not only is no grand jury going after Deal, Evans said, but he added that, "after inquiry, I was able to confirm that no grand jury has been convened."
In July, the Atlanta Journal-Constitution said a grand jury subpoenaed documents in May from state Revenue Commissioner Bart Graham.
The AJC said the papers were related to Graham's meeting with Deal and others about Deal's business arrangement with the state.
He co-owned a Gainesville salvage yard that - among other businesses - had no-bid arrangements with the state to provide space for inspections of rebuilt vehicles.
The newspaper said Deal tried to stop Graham and other officials from putting the program out to bid.
But Deal said his main complaint was Graham wanted to discontinue safety inspections on rebuilt vehicles. He's produced sworn statements by others that support his contention.
The Office of Congressional Ethics investigated the matter; its preliminary report said Deal may have broken several congressional ethics rules. But Deal resigned before the matter could be resolved.
Evans rejected the Barnes campaign's claim that Deal quit to abort the investigation, not - as he said - to have more time to stump for governor.
"I told him last year he could end the whole thing by stepping down," Evans said, noting the preliminary report wasn't filed early this year.
"He said, 'I'm not going to because I didn't do anything wrong.'"
Deal resigned in March after casting - as he'd vowed to do -a nay vote in a close showdown on the national health care bill.
Evans said the U.S. attorney's office can subpoena documents - such as those it reportedly got from Graham - without convening a grand jury.
Barnes campaign responded to Evans with a new attack on Deal. And it repeated a demand that he - as Barnes has - release tax returns for the last 25 years.
Barnes spokesman Emil Runge cited a finding by Citizens for Responsible Ethics in Washington, which filed the complaint that led to the inquiry by the congressional ethics office.
"Deal has been named one of the most corrupt members of Congress," Runge said, "and he fled Washington, D.C., because he was facing a congressional ethics investigation into his sweetheart, no-bid state contract.
"Just what is Nathan hiding in his corporate and personal income taxes? Georgians want an honest and experienced governor who doesn't need on-the-job training."
Deal spokesman Brian Robinson said Evans' statement "speaks for itself" and is "accurate."
Asked when Deal will release returns, he stood by what he said earlier this week: "It'll be soon and you'll know when it happens."
Even before Runge's potshot, Robinson had composed one of his own - to be used "if they have something snarky to say."
He cited Barnes' 2002 defeat for re-election.
"Roy Barnes," he said, "wants to talk about anything ... but why he was fired for cause and his big-spending, tax-hiking, job-killing agenda for Georgia.
"For now, we're happy for Roy to waste the money he's gotten from other people - as liberals are known to do."