Morata, who moved to Stamford Bridge from Real Madrid last summer, started in their opening game against Huddersfield which they won 3-0.
However, the Spaniard has struggled to find the net, and according to Sarri, this could be causing him confidence problems.
Morata is likely to be in the line-up against Arsenal on Saturday, and the Chelsea boss believes that if he gets a goal, he will get back on track.
Speaking in a press conference ahead of Chelsea's derby match versus Arsenal, Sarri said:
"I am not worried about Morata. He is a very great player."
"In this moment he needs to only gain confidence. He is a great player."
When Sarri was asked whether he thought Morata lacked confidence, he replied:
"Maybe. He needs to score. Like all the strikers in the world."
"He is improving so I am not really worried about him."
Arsenal visit Chelsea this weekend, and Sarri expects it to be a tough match, despite Emery's loss against Manchester City.
"Emery is a very good coach. He won three times the Europa League, he won in France with PSG."
"I think Arsenal will be competitive, they will fight for a place in the Champions League."