Star boxer Vasyl Lomachenko is turning down a title fight with George Kambosos Jr. ... all so he can stay in Ukraine and help his home country fend off a Russian invasion.
Promoter Lou DiBella announced the decision to ESPN's Mike Coppinger on Monday ... explaining the planned June 5 Lomachenko vs. Kambosos tilt is now off while Loma continues to take up arms in Ukraine.
Lomachenko, of course, has been front and center in the country since Vladimir Putin decided to invade the land back in February.
Just days after the war began, Lomachenko was seen holding a rifle and wearing army fatigues ... and he's been in the country fighting ever since.
Kambosos said Monday he respects Loma's decision to pull out of the planned boxing match -- saying in a tweet, "I totally understand and I pray for you and your country."
Kambosos added, "Please stay safe," and promised to remake the fight down the road.
Star boxer Devin Haney, meanwhile, is now expected to be tapped to fill in for Lomachenko.