The West London outfit will take on the Spanish giants in the first leg of the showdown at Stamford Bridge on February 20.
Messi, who has won five Ballon d'Or awards, has had a miserable time against Chelsea in the past having failed to score on eight occasions.
Morata, though, thinks that things could be different when the two clubs go head to head next week.
"Messi can't be stopped," the Spaniard told Movistar+. "If we can get a good result here, we have to play a defensive game with spaces and try to bother them as much as possible."
The return leg is scheduled for March 14 at Camp Nou.