The Republican presidential nominee suggested on RT that Democrats were behind claims Russian intelligence agencies had hacked their computers.
Mr Trump has faced a backlash since praising Russian President Vladimir Putin at a Wednesday night forum.
His Democratic rival, Hillary Clinton, accused him of being unpatriotic.
Mr Trump was interviewed on Thursday night by Larry King, a former CNN host who now presents a show on RT America, a Russian-funded TV network.
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When King asked him about reports that Russia is trying to disrupt the US election, Mr Trump was sceptical.
"I think it's probably unlikely," he said. "I think maybe the Democrats are putting that out.
"I hope that if they are doing something, I hope that somebody's going to be able to find out, so they can end it, because that would not be appropriate at all."
A Trump spokeswoman, Hope Hicks, suggested Mr Trump did not realise King's show was part of a Russian-backed network.
"Mr Trump recorded a short interview with Larry King for his podcast as a favour to Mr King," she said.
Why Trump strikes a chord with Russians
"What Larry King does with the interview content is up to him. We have nothing to do with it."
Back in the late 1980s and 1990s, Larry King was a titan of US political media. A guest spot on his television call-in show provided current and aspiring candidates a way to reach a national audience in a low-stress, friendly environment.
Donald Trump, back when he was just a larger-then-life real-estate developer and New York socialite, was a regular on King's programme. It's not entirely surprising then that the Republican nominee accepted an interview request from his long-time friend.
That, however, is when Mr Trump's staff should have done a bit of research, found out the interview would be broadcast on RT and told their candidate to come up with a scheduling conflict and politely pull out. Given the heat Mr Trump has taken recently for showering praise on Russian President Vladimir Putin, Russian-owned RT is the last outlet he should be on.
This is either another example of the Trump team's questionable advance work or - perhaps more troubling - its judgement. No matter the explanation, the story re-enforces the politically damaging perception that Mr Trump is uncomfortably chummy with the Russian government.
Private cyber-security analysts have blamed Russian intelligence agencies for electronic break-ins into Democratic Party computers that emerged in leaks over the summer.
Earlier this week Defence Secretary Ash Carter said the US would not ignore Russia's "efforts to interfere with our democratic processes".
During a televised forum on Wednesday on national security, Mr Trump complimented Mr Putin for having "great control over his country".
Mr Putin has offered kind words for Trump in the past, too, describing him as "a talented man".
The Republican chairman of the Senate Foreign Relations Committee, Bob Corker, offered words of caution for Mr Trump on Thursday.
"One has to be a little careful to let flattery affect one's judgment," he told CNN.
"Let's face it, over the last several years, President Putin has operated in ways that very much have been against our interests."
Mr Trump urged the Russians in July to hack into Mrs Clinton's emails to find messages that were deleted from her account amid an investigation into whether she abused state secrets.
In a news conference on Thursday morning at a New York state airport, Mrs Clinton invoked conservatives' most revered US president as she pounced on Mr Trump's remarks.
"What would Ronald Reagan say about a Republican nominee who attacks American generals and heaps praise on Russia's president?" she asked.
Donald Trump has told a Kremlin-funded TV network "it's probably unlikely" that Russia is trying to influence the US election.