Morata, who moved to Stamford Bridge from Real Madrid last summer, started last week’s opening 3-0 victory at Huddersfield, but failed to find the back of the net.
The Spaniard is likely to lead the line against Arsenal again on Saturday evening and Sarri says the 25-year-old needs a goal to get back on track.
Speaking ahead of the London Derby, 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.”
Asked if the former Juventus star was low on confidence, Sarri replied: “Maybe. He needs to score. Like all the strikers in the world. He is improving so I am not really worried about him.”