Novak Djokovic retired injured after losing the opening set of his clash with Alexander Zverev on Friday, sending the German to a first Australian Open final where he will take on defending champion Jannik Sinner for a maiden Grand Slam title.

Spectators booed as the 37-year-old Djokovic walked off toward the locker room, and he stopped, turned around and responded by giving two thumbs-up.

Novak Djokovic has reacted to the crowd at the Australian Open booing after he decided to retire from his semifinal against Alexander Zverev. The Serbian tennis player, 37, had taken to the court with his left leg heavily taped following Tuesday’s injury.

But, regardless of how you feel about him or what you think about him bowing out, nobody — not even Novak Djokovic — deserves to be booed for being injured. You don’t have to like him. You can absolutely root against him. You can boo him when he’s healthy.

A tennis master is forced to depart an Australian Open semifinal with an injury, riling some in the crowd. At 37, it may be harder than ever to bounce back.