Cape Town - Gilles Muller believes Novak Djokovic might be heading for another rough patch of form if he doesn't turn his attitude on court.
The recently retired ATP Tour star reckons Djokovic will struggle to overhaul Roger Federer's Grand Slam record if he get over his recent struggles quickly.
Federer has won 20 Grand Slams, more than any other man in history, although Djokovic has taken the last three to take his tally to 15.
However, the Serb has not looked himself other than the Australian Open this year, and Muller says hay be repeating a damaging old pattern.
"I thought the way that Djokovic was playing at the beginning of the year, he would maybe have another year where he would dominate as he did in the past," said Muller.
"But then I thought he was struggling again in Indian Wells and Miami.
"He didn't look very positive to me on the court. Didn't have positive energy or positive attitude.
"It reminds me of a couple of years back when he had the same thing, he won the French Open in 2016," he said.
"After that, you always felt he was in a bad mood and wasn't happy on the court.
"It seemed like the same way in Indian Wells and Miami," he said.
"So it depends on how he is. If he has a couple more years like last year, I think he's one that's going to break the record.
"But there is a long way to go."