Kyrgios must muscle up

NICK Kyrgios must get fit or risk falling short of his potential, according to French Open winner and Australian tennis great Ken Rosewall.

On the 50th anniversary of his second Roland Garros triumph, the first of the Open era, Rosewall issued a warning to the Australian No.1 – get fit or fall behind.

“In some ways, he’s his own worst enemy,” Rosewall said.

Kyrgios is battling an elbow injury which could yet force him to withdraw from the claycourt grand slam, which starts on Sunday.

The 23-year-old will test his fitness by playing doubles with American Jack Sock at this week’s ATP event in Lyon.

He’s missed six weeks on the tour and was last seen in action in Houston at the US Men’s Clay Court titles.