Donald Trump risks being a “loser president” if he wins November’s election and imposes a bad peace deal on Ukraine, Volodymyr Zelenskiy has said, saying it would mean the end of the US as a global “player”. In an interview with the Guardian in Kyiv, Zelenskiy said he had “no strategy yet” for what to do if Trump returned to the White House, and that the former British prime minister Boris Johnson had approached him on his behalf. If Trump beats Joe Biden, he is widely expected to cut off US military support to Ukraine. Last year Trump boasted he could end the war in “24 hours”. Trump’s aides have previously sketched out a possible plan that would involve giving Ukraine’s eastern regions to Russia, as well as Crimea. But Zelenskiy made clear that “Ukrainians would not put up with that”. Nor would they accept a Russian “ultimatum” that forced Ukraine to abandon integration with Europe and future membership of Nato, he said. Zelenskiy acknowledged that a re-elected Trump could, if he really wanted to, impose a crushing military defeat on Ukraine. He could cut off “support, weapons and money”, and even “make deals” with Kyiv’s partners so they stop deliveries of vital arms. “Ukraine, barehanded, without weapons, will not be able to fight a multimillion [Russian] army,” Zelenskiy told the Guardian. Speaking inside his presidential headquarters, he said he thought this scenario was unlikely. But he said if it happened there would be grave consequences for the US’s standing in the world – as well as for Trump personally. “Does he want to become a loser president? Do you understand what can happen?” Zelenskiy said. He predicted that Vladimir Putin would violate any Trump-brokered deal. “A ceasefire is a trap,” he said. After a pause Putin would “go further”, humiliating Trump and making him look “very weak” in the eyes of the world, he said. Zelenskiy continued: “This is not about him [Trump], as a person but about the institutions of the United States. They will become very weak. The US will not be the leader of the world any more. Yes, it will be powerful, first of all, in the domestic economy because it has a powerful economy without a doubt. But in terms of international influence it will be equal to zero.” Realising that Washington was no longer “a player”, other mostly authoritarian countries and leaders would “come into the arena” and emulate Putin’s aggressive “approach”, Zelenskiy suggested. And this would ultimately end in global disaster: “The beginning of what everyone is so afraid to talk about. This is reality. And this is the real third world war.” Asked whether Johnson had spoken to Trump on Ukraine’s behalf, Zelenskiy said: “I think he tried, and I think he spoke to him. I think so, yes, as far as I know.” He added: “I am sorry that I am using Boris as an instrument.” The initiative came as Kyiv lobbied pro-Trump Republicans in Congress and tried to persuade them to drop their opposition to Ukraine aid. The $61bn military aid package passed in April after a six-month delay. Zelenskiy made his comments a day before a New York jury on Thursday convicted Trump of all 34 counts of falsifying business records. The verdict in the hush-money trial made him the first former president to be found guilty of felony crimes in the US’s near 250-year history. In 2019, as president, Trump rang Zelenskiy and asked him to investigate his election rival Biden and Biden’s son Hunter. If Zelenskiy failed to find dirt on Hunter Biden, US security assistance to Ukraine would be withheld, Trump suggested, according to a leak of the call. The scandal led to Trump’s first impeachment. Zelenskiy said he had invited Trump to visit Ukraine. “I want to talk to him openly. I want him to come and see the war for himself. And then to talk to him. I think he would need it to understand the situation better,” he said. Zelenskiy said he understood that Trump “knows” Putin, based on the former president’s own “statements”. The pair have met at diplomatic summits. Trump has previously called Russia’s leader “a genius” and described his 2022 full-scale invasion of Ukraine as “pretty savvy”. Communicating with Putin was not the same as knowing him, Zelenskiy said, adding that to understand him better Trump should “see the results of what he brought to Ukraine” – a reference to the destruction of towns and cities, murders of civilians and the daily bombardment from Russian missiles.