Roger Federer SHOCK: You won’t believe who he could play at Hopman Cup TOMORROW

The 19-time Grand Slam champion is due to turn out for Switzerland against the USA at the Hopman Cup.

But, as it stands, Federer doesn’t have an opponent.

Jack Sock was scheduled to compete for America but he has fitness problems which forced him to retire during his clash with Japan's Yuichi Sugita on Tuesday.

Sock injured his hip after taking a fall during the first set of his men's singles clash.

It meant America were a man down for their doubles match which left Pat Cash to step in and partner the lady he coaches, Coco Vandeweghe.

And Cash, who is now 52, may have to pull on his gear again as tournament organisers still haven’t announced who will play him.

The Hopman Cup is an exhibition event which allows the rules to be relaxed, where it suits, to ensure fans get their money’s worth. He and Vandeweghe were beaten 0-4 4-3 (5-2) 4-0.

Cash said after his shock return: “I got warmed up nicely. I had a few games where I’m in my peak and then I’m over it. And that was in the first 10 minutes. Then it was downhill.”

Cash’s only Grand Slam title win came at Wimbledon in 1987.

Federer, meanwhile, won the tournament last season.