Novak Djokovic has promised to offer financial assistance to former Ukrainian player Sergiy Stakhovsky, who has joined Ukrainian troops to fight the Russian army.
"I'm thinking about you ... I hope everything will calm down soon. Tell me where can I send you help ... financial help or any other kind of help ...", wrote "Nole" in a WhatsApp conversation posted by the Ukrainian on Instagram.
The former world number 31 retired at the age of 36 following the Australian Open earlier this year before returning to Kiev to enlist.
Several other Ukrainian athletes have done the same, such as two-time Olympic boxing champion Vasiliy Lomachenko and former world heavyweight champion Oleksandr Usyk.
