Mr Trump on Wednesday said Mr Zelenskyy was "a dictator without elections" and falsely accused Ukraine of starting the war with Russia.
Nigel Farage has said Volodymyr Zelenskyy is not a dictator but called the UK and Europe "irrelevant" in peace talks aimed at ending the war in Ukraine.
The US president also claimed the Ukrainian leader has a 4% approval rating, but a report by the Kyiv International Institute of Sociology has said Mr Zelenskyy "retains a fairly high level of public trust" - about 57%.
Mr Farage said he would "suggest Europe and the UK government pay very serious attention to Donald Trump".
Other party leaders have strongly backed the Ukrainian president, with Sir Keir Starmer calling him to voice his support, telling him it was "perfectly reasonable" for Ukraine to "suspend elections during wartime as the UK did during World War Two".
