Djokovic dominated tennis from the middle of 2015 and he went on become the first man to hold all four Grand Slam titles at the same time after his success at the 2016 French Open.
The Serbian has constantly referenced that point in his career as the pinnacle while analysing his recent upsurge in form.
But world No 5 Zverev, who was easily beaten 6-2, 6-1 by Djokovic in the Shanghai Masters semi-finals yesterday, believes his opponent is now playing at a higher level than two years ago.
If Djokovic can continue his current form then he is on course to leapfrog Nadal to claim the year-end world No 1 ranking.
“I’m saying he’s playing — he’s probably the best player in the world right now,” Zverev said of Djokovic.
“He won back-to-back Grand Slams. He hasn’t lost a match since Toronto. He’s, for sure, the best player in the world.
“But, you know, I wish him nothing but the best. He’s definitely at the highest level he’s maybe ever been or maybe equal to it.
“I’m sure, as I said, if you ask him, he’ll say it was kind of a weird match.
“It wasn’t what probably both of us expected a little bit, just because I did too many early unforced errors, too many second serves, too many unreturned serves.
“All in all, it just wasn’t the best I could play. Nothing to do about that.”
Zverev’s defeat to Djokovic took only an hour and he was disappointed at not getting the basics right.
“I did, what, 24 unforced errors and 7 winners? I don’t think I’m beating anyone with that, to be honest,” added Zverev.
“Especially Novak. I was also serving under 50 per cent, and in the first set there is — I mean, there is no way of actually even competing with Novak, because, I mean, if you do that, he’s just too good.
“All in all, it was just — you know, obviously he’s playing great.
“He hasn’t lost a match in I don’t know how many months. He’s definitely playing well.”