Cassell, who signed SWP at 15 after he was released by Nottingham Forest, said: "I still think the Chelsea fans have yet to see the best of Shaun. His ideal position is in midfield and that is where he has had his best games for Chelsea rather than when he's played as a winger.
"When he plays in the centre he has many ways to get past people.
"Shaun is a great guy and a terrific player. He was the first player to break through at City after we had put the academy structure in place.
"People say I did well for him, but I always tell them they're wrong. He did more for us than we ever did for him."