The Serb lost his cool following questions over his conduct after he hit the ball into the crowd during his victory over Dominic Thiem at the O2.
Tim Henman claimed Novak Djokovic showed “where he is at mentally” with his angry outbursts at the Barclays ATP World Tour Finals.
The world No.2 hit a ball into the crowd in frustration after losing the first set of his opening match – and then petulantly responded to questioning in his press conference.
Former British No.1 Henman was famously disqualified from Wimbledon in 1995 for hitting a ballgirl with a ball in a fit of rage during a doubles match.
And the BBC analyst claimed Djokovic’s mistake wasn’t to lose his temper in the heat of battle – it was his tetchy post-match reaction.
“If it had hit someone then he would be have been disqualified,” Henman said.
“If he had just said, ‘You know, it was a mistake, I shouldn’t have done it. I was lucky I got away with it but it won’t happen again’, the story has gone.
“It is very surprising for a man of his experience but it does emphasis where he is mentally at the moment.”
Djokovic held all four Grand Slam titles after his defeat of Andy Murray at the French Open and led the Scot by more than 8,000 points at the top of the rankings.
But after a turbulent few months, his 122-week reign as world No.1 ended in Paris and now he needs to better Murray’s result at The O2 to end the year as the top-ranked player.
Murray’s former coach Miles Maclagan said: “He (Djokovic) has been frustrated in the second half of the season. He hasn’t quite been himself. I was shocked with what I saw.
“He’s definitely not himself.”
Djokovic was more like his old self after losing his first ever set to Dominic Thiem and lost only two more games in the match.
He will next face Kei Nishikori on Tuesday after the world No.5 beat US Open champion Stan Wawrinka 6-2 6-3 in only 67 minutes.
And the Swiss said: “Coming into the tournament, Novak wasn’t playing that good. But, again, it’s the World Tour Final. It’s a group qualification to make the semi-final. Novak won the first yesterday. Everything starts from zero.
“It was already an interesting match yesterday, watching Novak playing, winning, finding a better game than I think he played in the last few months.”