After a bright start to life at Stamford Bridge, Morata has had a difficult time in 2018, scoring just six times in the Premier League since the turn of the year.
Five of those goals have come this term, but his performances have been criticised, with the Spain international often appearing uneasy in front of goal and lacking in confidence.
Sarri believes Morata, 26, is similar to Saponara, who he coached at Empoli earlier in his career.
And Sarri feels Morata has the same type of mental fragility.
"It's difficult," Sarri said. "At Empoli I had a wonderful player, Riccardo Saponara, who we sold to AC Milan.
"Saponara was one of the best players I have ever seen, but a little bit mentally fragile.
"Alvaro has scored four or five goals in his last six matches, so I cannot see a big problem. I hope that there will be more this season.
"Every season he scores 15 or 16 goals, so he's around his average [goal return]. I speak with him every week, but on the pitch he is alone.
"I think that at the moment he's not playing to his full potential. It's difficult."
Chelsea signed Morata from Real Madrid in the summer of 2017 in a deal worth £60 million.
Last month Sarri expressed his doubts about the striker, who is battling Frenchman Olivier Giroud to be Chelsea's attacking spearhead.
He said: "I think Alvaro has a very great physical and technical potential, so I think he can improve more.
"He's a little bit fragile from the mental point of view. But he's very young. I think he can improve, improve very fast."