"Kyrgios has unbelievable potential," says King of Clay.
World No. 8 puts speed gun to test.
Two-time Wimbledon champion hopes to recover in time for Hopman Cup.
Olympic gold medalist to face 2012 Olympic silver medalist.
Hall of Famer can't confirm his return as coach in 2017.
Low-ranking players fixed matches in Spain and Portugal, say police.
World No. 10 has not named a coaching successor.
