Former world number one Djokovic, 30, will not play again in 2017 because of an elbow injury.
Cash said he could now "mentally refresh, get his enthusiasm back, and start back again strongly".
"We all know how tough and athletic he is, we want to see that again," the 52-year-old told BBC Radio 5 live.
"It might seem a bit obvious for a tennis player to get tennis elbow and there is literally no cure for it, it just takes time, usually about a year or so, to fix it.
"But it is probably just what the doctor ordered, to take time off. After so many unbelievable years, 2017 has been poor for him."
Djokovic retired injured during his most recent match, a Wimbledon quarter-final against Tomas Berdych on 12 July.
Earlier in the month, he won the Aegon International at Eastbourne - his 68th career title, but his first since January.
He suffered a shock defeat by world number 117 Denis Istomin at January's Australian Open, where he was defending champion, and then lost his French Open crown when he was beaten by Dominic Thiem in the quarter-finals in June.
"It will take time for him to get his intensity back," said Australian Cash, the 1987 Wimbledon men's singles champion.
"It won't be like Roger Federer, who was winning Grand Slams straight out of the blocks after he came back [after several months out with a knee injury in 2016], but some time next year he will be playing well again.
"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.
"He has probably lost two of those three major qualities, but he will be very sensible and make sure he is ready when he does come back. I do think he will be competitive again."
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Novak Djokovic's enforced break through injury will help the 12-time Grand Slam winner recover his best form, says former Wimbledon champion Pat Cash.