In 2013 he achieved one of the great shocks in tennis history, knocking defending champion Roger Federer out of Wimbledon.

Today, the Ukranian player Sergiy Stakhovsky is a volunteer fighter on a military patrol in Kyiv, which he vows to defend "to the end" against Russian forces.

Now 36, he looks much the same as the journeyman player ranked 116 in the world who lay stretched out in his tennis whites on the hallowed London turf after toppling Federer in the second round nine years ago.

But his outfit now could not be more different as he patrols Maidan Square, symbol of Ukraine's "fight for democracy", armed with a Kalashnikov, a pistol in his belt and his 1.93 metre (6 ft 4 in) frame dressed in khaki camouflage.

"I cannot say that I feel comfortable around a rifle. I am not sure how I am going to react to shooting at somebody," he tells AFP. "I wish I would never have to be preoccupied with these things."

It's been just over two weeks since he returned to Ukraine and signed up for the territorial brigade, the volunteers tasked with helping the army against the Russian invasion launched on February 24.

"I knew I had to go there", he says.