Simon Lingard's loved ones said he “died fighting for what he believed in”.
The Foreign Office said it was supporting the family of a British national who died in the war-torn country.
The Ukrainian military has offered to return him to England, Lingard’s relatives said.
But the family have also set up a fund-raising page asking for support to give him a fitting send-off.
“As most people are aware my dad, Simon Lingard, (Grimmy) sadly lost his life in Ukraine on Monday November 7," the family wrote on the GoFundMe page.
“My dad was an inspiration to all who knew him, a real-life hero who died fighting for what he believed in.
"He was loved and adored by so many, a true representation of what a soldier should be.”
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They described being “absolutely heartbroken” at their loss.
“The Ukrainian military have offered to bring him home to England but we need help to show him the respect and adoration he deserves by giving him the greatest well-deserved send-off," they wrote.
“Could you all please find it in your heart to donate anything, no matter how small, so we can honour our dad and allow him to finally Rest in Peace.”
A Foreign Office representative said: “We are supporting the family of a British national who has lost his life in Ukraine and we are in touch with the local authorities in connection with his death.
“Our thoughts are with their family at this difficult time.”
In June, former British soldier Jordan Gatley was hailed a hero by his family and an adviser to Ukrainian President Volodymyr Zelenskyy, after he was killed while fighting in Ukraine.
Gatley was shot dead in the city of Severodonetsk in eastern Ukraine.
He left the British Army in March and travelled to Ukraine to help forces there “after careful consideration”, his father said.
Gatley, who it is understood was a rifleman with the Edinburgh-based third battalion of The Rifles, was also praised by Mykhailo Podolyak, an adviser to Mrr Zelenskyy, who said he would always be remembered for his contribution.
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A small number of serving British personnel are believed to have gone absent without leave to join the resistance against the Russian invasion, while veterans and Britons without combat experience are thought to have also travelled to Ukraine.
There was initially confusion on the government’s position after then-foreign secretary Liz Truss told the BBC on February 26 that she would “absolutely” support UK nationals who chose to fight for Ukraine.
But she later withdrew from those comments, insisting she had been “expressing support for the Ukrainian cause” and that there were “better ways” to contribute to Ukraine’s defence.