The former Real Madrid striker has little doubt that his countryman still has more room for growth.
The 25-year-old was linked with a move away from Camp Nou last summer having struggled to find his feet after moving to the Blaugrana from Udinese in 2011.
Sanchez has already netted 11 goals in 14 La Liga appearances so far this campaign, including a hat trick in this weekend's 4-0 win over Elche, and Zamorano has been impressed with his resurgence.
"Alexis is going through a great period. He has been huge for Barcelona. He has not played at this level since his move to Spain," the former Real Madrid striker told El Mercurio. "He is starting to feel at home at Barca. It's not easy to adapt to life at such a big club. You have to fight against a lot of things in order to succeed.
"He has really grown as a player, but he still has room for improvement. Alexis can get even better. He is still young and has plenty to offer."
Sanchez will be looking to add to this tally on Wednesday when Barcelona host Getafe in the Copa del Rey round of 16.