Donald Trump appears to have backtracked on his controversial debate statement that he may not accept the result of the November election, now saying he will accept the result - but only if he wins.

The worrying comment caused something of a backlash, particularly as his VP running mate Mike Pence had previously assured voters the GOP nominee would accept their decision despite Trump stating he believed the election is rigged.

But a day after he told debate moderator Chris Wallace he would "keep him in suspense" about whether he would accept the election result, Trump jokingly told a rally in Ohio he would accept the results of the election if he won the White House.

"I would like to promise and pledge to all of my voters and supporters and to all of the people of the United States that I will totally accept the results of this great and historic presidential election, if I win," CNN reported Trump as telling the crowd.

"Of course, I would accept a clear election result, but I would also reserve my right to contest or file a legal challenge in the case of a questionable result," he added.

"And always, I will follow and abide by all of the rules and traditions of all of the many candidates who have come before me. Always."

His comments came after several high profile members of the GOP, including Senator John McCain - who recently withdrew his support for Trump - said it had been inappropriate of the nominee to suggest he would not accept the result.

"I didn't like the outcome of the 2008 election. But I had a duty to concede, and I did so without reluctance," McCain said in a statement seen by Politico.

"A concession isn't just an exercise in graciousness. It is an act of respect for the will of the American people, a respect that is every American leader's first responsibility."