Aleksander Kukin was "instrumental" in the creation of the Kyiv Reds supporters' club back in 2002 but he and his family have been caught up in the conflict.
He had been trying to flee the war-torn capital but his car came under fire by Russian invaders. He was killed in the attack.
His wife and daughter were wounded in the crossfire, and have since undergone operations in hospital.
In a statement, Manchester United said: "We send our heartfelt condolences for their loss and best wishes for their recovery, as they attempt to deal with these awful events.
"The club is exploring a number of ways in which it can offer its support to both Aleksander's family and the Kyiv Reds in due course."
A recent photo shared by the Kyiv Reds showed Kukin enjoying United's 4-2 win over Leeds just a few weeks before his death.
Supporters have taken to social media to pay tribute to Kukin's "energy and passion" for Manchester United.
One fan, Ivan, wrote: "He used to take me to games in the local pub in Kyiv and drive me home after the midweek games when I was a kid.
"[He] posted my United articles on [the] Ukrainian Reds website and helped the growth of that movement nearly single-handedly, paying from his own pocket. Great great Man."
A United memento was placed inside his coffin during his funeral and mourners sang: "He went to rest in Heaven with George Best."
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