Novak Djokovic was booed off the court by some Australian Open fans after retiring injured from his semi-final against Alexander Zverev.

Djokovic, who was bidding for a record-extending 11th title, quit after losing the first set 7-6 (7-5).

The 37-year-old Serb had his upper left leg heavily taped after injuring it in Tuesday's quarter-final win over Carlos Alcaraz.

After he slapped a volley into the net on set point, Djokovic immediately approached the net and shook hands with Zverev.

He waved to the crowd and gave them a double thumbs up, despite audible boos from some sections inside Rod Laver Arena.

"The very first thing I want to say is please don't boo when a player is injured," said Zverev in his on-court interview.

"I know everyone paid for tickets but Novak Djokovic is someone who has given everything to the sport.

"He has won this title with an abdominal injury, he has won this title with a hamstring injury.

"If he cannot continue a tennis match, he really cannot continue a tennis match."

German second seed Zverev is still bidding for his first Grand Slam title after twice losing in major finals.

In his first Australian Open final, he will face either Italian top seed Jannik Sinner or American 21st seed Ben Shelton.