John McEnroe gives his immediate reaction to Novak Djokovic's semi final retirement.

John McEnroe and John Millman say the crowd's reaction to Novak Djokovic's decision to quit his semi was 'disrespectful'.

John McEnroe and John Millman say the crowd's reaction to Novak Djokovic's decision to quit his semi was 'disrespectful'.

Ash Barty gives her take on Novak Djokovic quitting his Australian Open semi final and the crowd's reaction to him.

Ash Barty gives her take on Novak Djokovic quitting his Australian Open semi final and the crowd's reaction to him.

Ash Barty gives her take on Novak Djokovic quitting his Australian Open semi final and the crowd's reaction to him.

Jim Courier and John Millman unpack what Novak Djokovic's future in the sport holds after his sudden retirement at the Australian Open.

Jim Courier and John Millman unpack what Novak Djokovic's future in the sport holds after his sudden retirement at the Australian Open.

Novak Djokovic's pursuit of a 25th Grand Slam title ended as he retired injured during the Australian Open semi-final against Alexander Zverev....

Novak Djokovic stages a hilarious reaction to the electric line-calling system working in his favour.