The 12-time Grand Slam champion announced his decision to take the rest of the year off last week after he bowed out of Wimbledon a wounded soldier.
Djokovic retired a set down to Tomas Berdych in the quarter-finals at SW19 last month and will skip the remaining three months of the year – including the U.S. Open – to recover.
But Cash does not believe it signals the so-called decline of the Serb and instead says he will come back both physically and mentally stronger.
‘So many unbelievable years’
“It will take time for him to get his intensity back,” the Aussie told the BBC.
“Djokovic's style is very similar to almost everyone else on the circuit, but he was just that bit fitter, that bit more flexible, that bit more mentally tough.
“It is probably just what the doctor ordered, to take time off. After so many unbelievable years, 2017 has been poor for him.”
Djokovic has struggled since he became the first man since Rod Laver to hold all four Grand Slam titles simultaneously at the French Open last year, surrendering his position atop the ATP singles rankings to Andy Murray after a dismal end to 2016.
Roger Federer had a similar injury lay-off in 2016 and returned earlier this year to sweep all before him, but Cash believes Djokovic will take time to settle into his familiar rhythm.
“It won't be like Roger Federer, who was winning Grand Slams straight out of the blocks after he came back, but sometime next year he will be playing well again,” he added.
“He will be very sensible and make sure he is ready when he does come back.”