Elina Svitolina has penned an emotive letter to her homeland of Ukraine, pledging to donate her prize money to military and humanitarian needs after Russia's invasion.
Russia invaded neighbouring Ukraine on Thursday. That conflict has escalated over the weekend.
Russia and Vladimir Putin's government faces heavy political and financial sanctions, while sports organisations such as the International Olympic Committee (IOC) and UEFA have also condemned the attack.
St Petersburg has been stripped of this season's Champions League final, while Poland, Sweden and the Czech Republic have refused to play Russia in qualifiers for the upcoming FIFA World Cup. Formula One has pulled the Russian Grand Prix from its race calendar for 2022.
Several tennis players have spoken out against Russia's aggression, including Russian duo Andrey Rublev and Daniil Medvedev, who will ascend to world number one in the ATP rankings on Monday.
On Saturday, Svitolina – the former WTA world number three – told Sky Sports News she was "shocked at this terrible nightmare".
Svitolina has family and friends back in Ukraine and, on Sunday, she posted an emotional message on her social media channels.
"Letter to my Motherland, I am currently far away from you, out of sight from my loved ones, far from my people, but my heart has never felt so warm and filled of your soul," Svitolina's message read.
"It is difficult to express how special you are. To me you are strong, beautiful and unique. You gave me everything and I cherish every piece of you: your culture, your education, your lands, your seas, your cities, your people. My people.
"My people, every day I fear for you. I am devastated, my eyes won't stop crying, my heart won't stop bleeding. But I am so proud. See our people, our mothers, our fathers, our brothers, our sisters, our children, they are so brave and strong, fighting to defend you. They are heroes.
"I commit to redistribute the prize money of my next tournaments to support army and humanitarian needs and help them to defend you, our country.
"Ukraine, you unify us, you are our identity. You are our past and our future. We are Ukraine."
Svitolina also called on other nations to continue to step up their efforts to stop the invasion.
"May the world see it and help us to join forces to protect you," she wrote. "You are in all my thoughts and prayers. You are always with me. I am Ukraine. We are Ukraine."