Colombian great Ivan Zamorano has been in Italy this week.
Zamorano took in Lazio's win against Fiorentina on Sunday.
He later told Lazio Style Radio: "I knew (Taty) Castellanos when he played in the United States, he left a memory beautiful in the MLS. Then he was at Girona and now at Lazio, he is a great player and a great person.
"Serie A is a difficult championship, I played for 5 years here at Inter and I always say that the striker who is suited to Serie A, he can play anywhere. It's a very tactical league, it's difficult to adapt to the coach and the defensive style.
"Taty came from a freer Spanish football, here you work a lot more. His adaptation has been good, he is fine and can be very useful and important at Lazio. He is an intelligent player.
"When you have a coach like (Maurizio) Sarri who understands if a player can be suited to his style, then Castellanos can be a very important player. A coach like Sarri can improve your players. Taty must take advantage of these coaches who can be very important for his career."