Ukrainian Ambassador to the UK Vadym Prystaiko had been dismissed, with Kiev's Foreign Ministry giving no official reason for his sacking, British media reported on Friday.
One British news website claimed that the ambassador had been on the receiving end of a "very strong" telephone call from Kiev.
A diplomatic source told a UK news agency that the reprimand was over his public criticism of Zelensky's response to British Defence Secretary Ben Wallace's comments at last week's NATO summit.
"I believe it was responded with a little bit of sarcasm, President Zelensky said that each and every morning he will wake up and call Ben Wallace to thank him," Prystaiko said in an interview with a British TV news channel on July 13. "I don’t believe that this sarcasm is healthy."
Last week, Wallace said that Kiev had treated him like online retail delivery service Amazon, giving him shopping lists of armaments. He hit out that Ukraine should show more gratitude.
That followed Zelensky's angry attack on NATO for refusing to admit Ukraine as a member while its conflict with Russia continued. The Ukrainian president later hit back at Wallace, mocking his comments.
"How else can we show our gratitude? We can wake up in the morning and thank the minister. Let him write to me and tell me how to thank him," Zelensky told a press conference.
Wallace has since announced he will be stepping down from his ministerial job at Prime Minister Rishi Sunak's next cabinet reshuffle, expected soon, and exiting politics at the next general election in 2024 or 2025.
That was after the PM contradicted the defense secretary, insisting that Zelensky "had expressed his gratitude for what we’ve done on a number of occasions."
It was not the first time that Ukraine's outspoken ambassador has put his foot in it. On March 4, Prystaiko told a US government-run propaganda radio station that Britain would double the number of Challenger 2 tanks it was donating to Ukraine from 14 to 28. That prompted a swift denial from London.