An injured Novak Djokovic has quit after dropping the first set of his Australian Open semifinal against Alexander Zverev.

Djokovic sustained a muscular injury in his titanic tussle with Carlos Alcaraz earlier this week, and came onto the court at Rod Laver Arena on Friday with heavy strapping around his left leg.

Alexander Zverev said he felt ready to challenge for a long-awaited Grand Slam title at the Australian Open after being ...