That is the view of Amazon Prime pundit Barry Cowan.
The German gets his Cincinnati Masters campaign underway later against Serbian Miomir Kecmanovic in the second round.
Zverev has never won a match in Ohio, having lost all four of his matches all in three sets.
“It’s a place where I’ve never won a match so far in my life, but I hope I can change it now and hopefully make a deep run here,” he said.
After winning the ATP Finals last November, Zverev has failed to live up to the added scrutiny, especially in the Majors.
He has also recently split with Ivan Lendl as his coach after a turbulent relationship.
Speaking ahead of Zverev’s clash with Kecmanovic, Cowan expressed his worries about the 22-year-old.
“His form at the moment is worrying,” he said.
“I’m actually really concerned about Zverev at the moment. His last four matches he’s played, he’s hit 36 double faults.
“He is actually missing 29 per cent of second serves he hits.
“So it doesn’t matter how hard you fight and Zverev fights for every single point, eventually that’s just going to get you down mentally.
“And I think we saw that against [Karen] Khachanov on Friday when I couldn’t believe how poorly he started that match.”
When asked about the causes of Zverev’s woes, Cowan added: “I think it is technique.
“I think he collapses on that second serve. A lot of the second serves end up going in the net.
“At six foot six, he needs to stay up on that serve.
“On the second serve, it is the same racket serve acceleration as your first serve. The difference – a bit more spin.
“And at the moment we see different second serves from Sascha. We see one at 125mph that is flat and he misses it long.
“And then we see the one that is 85mph that he decelerates and goes halfway up the net.
“He needs to get that sorted first because otherwise, he’s just going to go match after match with that area of this game failing him.”