Sergiy Stakhovsky beat defending champion Roger Federer at Wimbledon in 2013Ukrainian tennis player Sergiy Stakhovsky says he hopes he will not have to use the gun he has been given after signing up to help his nation's defence against the Russian invasion.
Boxer Vasiliy Lomachenko, a three-weight champion, is another sports star to join Ukraine's reserve forces and has been photographed with a rifle.
Heavyweight boxing champion Oleksandr Usyk is also thought to have signed up.
Stakhovsky said: "I know how to use the gun. If I'll have to, I'll have to."
The 36-year-old retired from tennis after the Australian Open in January and has returned to Kyiv to help his nation's defence.
Reigning heavyweight champion Usyk, who beat Britain's Anthony Joshua in September, has left his London base to go back to Ukraine.
Photographs on Instagram - from an unverified Ukraine Boxing Federation account - claim to show the 35-year-old holding a weapon.
Lomachenko, 34, was shown wearing military uniform with a rifle across his shoulder in a post on his Facebook page.
Men between the ages of 18 and 60 have been told by the Ukrainian government to stay in the country and fight as it looks to slow Russia's attacks.
"I pretty much hope that I won't have to use the gun," Stakhovsky, a former world number 31 known for beating Roger Federer at Wimbledon in 2013, told BBC Radio 4's Today programme.
Stakhovsky has left his wife Anfisa and children at their home, saying it was a "horrible" decision to make.
He thinks Anfisa has told their children he has gone to another tennis tournament.
"I'm still not sure how I've done it. I know that it's extremely hard on my wife. My kids don't know that I'm here," he said.
"They don't understand war. They're too little to understand what's going on."
Will sporting sanctions make a difference?
Sporting organisations are continuing to impose sanctions on Russian teams and athletes after the country, supported by Belarus, launched a military invasion of Ukraine last Thursday.
On Monday, Russian football clubs and national teams were suspended from all competitions by Fifa and Uefa "until further notice".
It means the Russian men's team will not play their World Cup play-off matches next month and the women's team have been banned from this summer's Euro 2022 competition.
Spartak Moscow have been kicked out of the Europa League, while Uefa has ended its sponsorship with Russian energy giant Gazprom.
The International Olympic Committee has urged sport governing bodies to ban Russian and Belarusian athletes.
The Ukrainian Tennis Federation has called on the sport's governing body, the International Tennis Federation (ITF), to expel Russia and Belarus from the organisation and ban Russia from individual and team tournaments.
Ukrainian world number 15 Elina Svitolina has said she will refuse to play Russian or Belarusian players until they are classed as 'neutral athletes'.
Stakhovsky says he believes these moves will make "a lot of difference in terms of perspective" for Russian President Vladimir Putin.
"He really loves sport and loves that Russia is successful in sport. He loves that he can demonstrate that success out in the world during the Olympics and all the other sport events," said Stakhovsky.
