Wladimir Klitschko recorded a video message from Ukraine which was shown at Wembley Stadium ahead of Tyson Fury v Dillian Whyte on Saturday night.
The former world heavyweight champion is currently in his native country, where Ukrainian forces are defending against the Russian invasion.
Earlier this week, the WBC announced the “OPUS Book of WBC’s Greatest Fights”.
Among the special editions of this book, there is one devoted to peace in Ukraine, which will benefit the official humanitarian fund.
Klitschko said in his post: “I wish I could be with you tonight in London, but as you know we have our own flight here.
“This is the most important fight of our lives.
“We take this opportunity to thank all of our friends and partners around the world, especially the WBC family and Opus for all the support and fundraising efforts with the WBC Great Fights Ukraine Peace Special Edition.
“The challenges we face every day are the greatest of our lives, but we are stronger knowing we have your support.
“All of your help is needed and appreciated for the mothers, fathers and children of Ukraine.
“Please don’t stop because we need you more than ever. Good night to all of you in London and cheers from Kyiv.
talkSPORT will bring you live coverage of the huge world heavyweight title fight between Tyson Fury and Dillian Whyte at Wembley on Saturday night, with our coverage starting at 7.30pm and featuring expert analysis from Ben Davison’s ringside