The WWE has kept its distance from McMahon's campaign, though it has responded independently to claims from former wrestlers about the company's practices during McMahon's tenure.
The WWE said it was unlikely that Cade would reveal information on steroid use to "a total stranger."
"It is very dubious that [Nowinski] ever had a conversation with Lance Cade, much less Lance Cade confiding to a total stranger that he used painkillers and steroids," the company said in a statement.
McMahon has not shied away from her past as CEO of the WWE, even highlighting her experience with the company in campaign ads. But the death of Cade and the lingering questions about the WWE's work practices threaten to turn the association into a negative one.
When asked about Cade's death last week, McMahon said that the company can no more be held accountable for Cade's death "than a studio could have prevented Health Ledger’s death," referring to the Australian actor who died of a drug overdose in 2008.
"Who knows what causes people to have addictions and do what they do?" McMahon said.
When contacted by The Hill, Nowinski said he was surprised to have the WWE question his relationship with Cade. "They don't think I've ever met my 2003 tag-team partner in the WWE developmental system, who I worked with in Cincinnati and Louisville in 2002-2003 almost daily and saw regularly while working with WWE until 2007?" Nowinski said.
"Linda [McMahon] can spend $24 million on a campaign, you'd think they could hire a decent PR person," he added.
Nowinski, who is now an expert on concussions, said he felt the need to speak out because of McMahon's public position. "When someone would disrespect a deceased former employee, when she's seeking [a Senate seat], as a patriot you have to say something," Nowinski said. "You want to make sure good people are in those jobs."
A spokesman for McMahon said the campaign hasn't commented on Nowinski’s allegations.
Nowinski isn't the first former wrestler to question McMahon's leadership of the WWE. After McMahon launched her campaign last year, several former wrestlers — including stars such as Bruno Sammartino and Billy Graham — spoke out against her.
McMahon said Graham was a "self-confessed liar," and dismissed Sammartino as someone who has "still got sour grapes because he didn’t make as much money as the guys today are making."
"You're going to always have the old-timers who are going to come out and say [things]," she said. "It's just not like that."
In its statement responding to Nowinski, the WWE noted that at "no time does he ever state that it was suggested that he" take steroids.
Nowinski said the push to take banned substances at the WWE was implicit.
"The point I was making was that they reward people who take steroids," Nowinski said, adding that performers who do get "top billing."
Nowinski admits he can't prove that Cade told him he was using steroids. "I can never prove I had that conversation with Lance because Lance died when he was 29 years old," he said. "They want to call me a liar — the person who can confirm it is dead after he worked for them for [almost a decade]."
The WWE's statement noted that Nowinski said it was "unsafe" to perform in the ring and yet desired to do so. Moreover, Nowinski "did not reveal, as required, that he suffered previous concussions before signing his contract with WWE," according to the release.
Nowinski said he "was unaware that I had a concussion history until the last one."
He also told the New England Cable News that performers wrestle 200 times a year, a claim the company called "not factual."
"In 2009, the average active roster talent performed 135 days," according to the WWE.
Nowinski said there's a difference between the average number of days a wrestler works and the range.
"Not every talent performs 200 days a year," he said. "I may have rounded up."