Former Russia captain Igor Denisov labelled the ongoing Ukraine invasion a "complete horror", but fears he may be jailed or killed for speaking out.
Russia, with the help of nearby Belarus, invaded neighbouring Ukraine in late February after weeks of heightening political tensions between the two countries.
The actions of Russia have led to widespread condemnation, with financial, sporting and political sanctions imposed on the nation in an attempt to deter the attacks.
Football stars such as Oleksandr Zinchenko and Andriy Shevchenko have repeatedly called for the invasion to stop, but Denisov is one of the most prominent Russian athletes to condemn the attacks.
Former Zenit midfielder Denisov, speaking to sports journalist Nobel Arustamyan in an interview published on YouTube, is still living in Russia and acknowledged he is risking his life by opposing the invasion.
"To me, this war is a catastrophe, a complete horror," said Denisov, who captained his country and earned 54 caps between 2008 and 2016.
"Maybe they'll put me in jail or kill me for these words, but I'm telling it like it is."
The 38-year-old also revealed he has personally written to Russia president Vladimir Putin to urge the attacks to stop.
"I am a proud guy. This was after three or four days," Denisov added. "I even said to him that I am ready to go on my knees before you so that he would stop it all."