Oleksandr Usyk has urged the International Olympic Committee (IOC) not to allow Russian and Belarusian athletes to compete at the 2024 Olympics under a neutral banner, saying any medals they win will be "medals of blood".
The IOC last month pledged to "explore a pathway" for Russian and Belarusian athletes to compete as neutrals in Paris, stating "no athlete should be prevented from competing because of their passport".
Russian and Belarusian athletes are currently banned from Olympic competition after Vladimir Putin's regime launched an invasion of Ukraine last February.
Ukraine has threatened to boycott the games if Russian and Belarusian athletes are allowed to take part, while several other nations have supported calls for the countries to remain excluded.
Mayor of Paris Anne Hidalgo recently backed suggestions their athletes could compete under a neutral flag, although she has since backtracked on the comments, saying: "It is not possible to parade as if nothing has happened".
In a video posted to his Instagram account, Usyk addressed IOC president Thomas Bach directly, adding his voice to calls for the countries to remain sidelined.
"Dear Mr Bach, I would like to address you," Usyk said. "I am a Ukrainian athlete; I won an Olympic gold in boxing in 2012. I am the current world heavyweight champion and my name is Oleksandr Usyk.
"You want to allow Russian athletes to compete at the Olympics. Russian armed forces invaded our country and kill civilians.
"The Russian Army is killing Ukrainian athletes and coaches and destroying sports grounds as well as sports halls. The medals that Russian athletes are going to win are medals of blood, death and tears.
"Let me wish that you have a peaceful sky above you and for you to be in good health and happy."
Sanctions imposed by the IOC against Russia and Belarus include no international sports events being organised or supported in either country by a National Olympic Committee, while no sports meeting or event is allowed to fly Russian and Belarusian flags or colours.