Crespo won the Premier League title during his time at Stamford Bridge.
"I think he is a great player," Crespo told Goal.com. "He is a young player who has a lot of trophies already.
"However, you need to be patient. He has showed he is a very good striker, but normally when you play in a big team it is difficult to be at a high level for the whole year. In the past, the same thing happened at Juventus, but that is because he is young.
"He can be the future of Chelsea but it depends on him. It is important to see if he is happy. If he is happy at Chelsea and he can show his best in this team then it would be great for everyone, but if he wants to come back to Juventus and make another experience then we will see.
"It is different than my experience at Chelsea because I was older than him. I had already been past my best level. The Premier League at that time wasn't the best in the world. Now it is. At that time, when I played, Serie A was actually the best. Then, AC Milan called me, the second time was Inter."