The outgoing US President has told the Republican nominee to "stop whining" about the possibility that the election could be rigged.
Trump has stepped up his attacks on his rival Hillary Clinton over the last week, accusing her of colluding with the media to fix the outcome of the election.
Of course there is large scale voter fraud happening on and before election day. Why do Republican leaders deny what is going on? So naive!— Donald J. Trump (@realDonaldTrump) October 17, 2016
Ahead of the final presidential debate tonight, Obama told Trump his arguments were "based on no facts".
"I'd advise Mr Trump to stop whining and try to make his case to get votes," Obama said last night. "If whenever things are going badly for you and you lose, you start blaming somebody else, then you don't have what it takes to be in this job."
Read more: Polls looking worse for Trump
Obama also attacked Trump's "continued flattery of Mr Putin", the Russian president.
The election is absolutely being rigged by the dishonest and distorted media pushing Crooked Hillary - but also at many polling places - SAD— Donald J. Trump (@realDonaldTrump) October 16, 2016
Trump has experienced plummeting poll ratings in the past few weeks after facing accusations of sexual assault. Yesterday his wife went on CNN to fight his corner and defend his "boy talk", saying he was a "gentleman".
But it seems that some Americans have been persuaded by his comments, as a new poll shows 41 per cent of US voters believe the election could be "stolen" from him.
However, betting firm Paddy Power said yesterday they would be paying out on people who have placed bets on Clinton to win the presidency, saying the election is now a done deal.