Morata endured an underwhelming debut season with the Blues following his £65m move from Real Madrid, and he has scored just one goal so far this season too.
The Spaniard lost his place in the starting XI for Chelsea's last Premier League outing against Cardiff - during which his replacement Olivier Giroud registered two assists - and Sarri admitted that he is unable to help Morata regain the confidence he needs after another goalless showing against PAOK on Thursday night.
"Alvaro Morata has to gain confidence with one, two, three goals. I am not able to give him confidence. In this match he has had three, four opportunities. He was unlucky," Sarri told talkSPORT.
"I hope for him that in the future I can try to help him, but the confidence can come only with goals.
"I have to say also, for maybe the first time in this season Alvaro was ready in the box. He was on the ball and was active."
Morata scored 15 goals in 48 appearances for Chelsea last season.