Former tennis player Alexandr Dolgopolov said on Wednesday he has traveled home to Ukraine to defend the country after undergoing weapons training.
The 33-year-old, who won three ATP titles and reached a career-high ranking of number 13, said he was in Turkey with his sister and mother when Russia's invasion of Ukraine began.
"I already started practicing shooting, and I was very lucky, that a ex professional soldier taught me for 5-7 days," Dolgopolov wrote on Instagram.
"Once I found a few guys planning to go to Ukraine from the US ... we started our travel. Took some bulletproof vests for us and our army, flew to Zagreb ... and I drove through Europe, and entered Ukraine from Poland, and at last, I am in Kyiv.
"This is my home, and we will defend it! With all the people that stayed! I will stay in Kyiv until our victory and after."
Dolgopolov also posted a picture of a gun and military gear on Twitter, with the caption "used to be rackets and strings, now this."
Former tennis player Sergiy Stakhovsky enlisted in Ukraine's reserve army last month, while boxers Oleksandr Usyk and Vasiliy Lomachenko joined territorial defense battalions.
Ukraine's former world heavyweight champions Wladimir Klitschko and his brother Vitali, who is now mayor of Kyiv, have also both vowed to take up arms against invading Russian forces.
Russia calls its actions in Ukraine a "special operation" designed not to occupy territory but to destroy its neighbor's military capabilities and capture what it regards as dangerous nationalists.