He said he based that prediction on what he deemed a "poor showing" by the Republican Party in the midterm elections. On top of that, Mahathir told CNBC's Sri Jegarajah, Trump's leaving office would end any potential for the "very disruptive trade war" to continue in the years to come.
"As you can see from the midterm elections, he has not done so well. The chances of him getting a second term is a bit bleak at the moment ... I will be surprised if he's re-elected after his poor showing in the midterm elections," the 93-year-old leader said.
The November elections were widely seen as a referendum for Trump and his policies. The Republican Party — which controlled both the Senate and the House before the election — lost the House majority to the Democrats.
"If Trump is not there, the other members of the U.S. government, whether they are Republican or Democrat, they will not continue with this very disruptive trade war," Mahathir added, referring to the tit-for-tat tariff fight between the U.S. and China.
Trump's presence in the White House will determine how far the ongoing tariff fight will go, the Malaysian leader said. He added he's not sure the expected G-20 meeting between Trump and Chinese President Xi Jinping would yield any compromise or breakthrough in the trade tensions between the world's two largest economies.
Malaysia is a trade-dependent economy, with exports of goods and services accounting for more than 70 percent of its gross domestic product, according to data by the World Bank. Economists have pointed out that the country would be vulnerable if the tariff fight escalated and then reduced global trade.
"With Trump, you can't predict anything, we don't know how he will react," said Mahathir.
That's not the first time the Malaysian leader has publicly criticized the American president. Mahathir previously urged Trump to be "consistent" and also said the president's style was hurting U.S. efforts in Asia.
Trump has skipped several summits with Asian leaders since he took office, and will not attend another gathering in Singapore this week. Instead, Vice President Mike Pence will be present at the summit with leaders from the 10-member Association of Southeast Asian Nation.
"It doesn't bother me," Mahathir said of Trump not attending the summit. "Because I don't know what he's going to say and he's not committed."