Hoops boss Neil Lennon revealed last night the club had rejected a second bid from Norwich.
Lennon also confirmed Hooper - who has 18 months left on his deal - had turned down a new contract offer but the manager was confident he would still be a Celtic player on February 1.
However, Caldwell - who quit Parkhead for Wigan in January 2010 - believes any club that does succeed with a bid will secure themselves a bargain.
He said: "Having seen the players down in England, I think he would do really well, he would score a lot of goals.
"If you do that in England, there is really no price that you can put on it if you can score enough goals for your team.
"The clubs who are looking at him now would definitely get a bargain.
"I'm sure if he went down there and started scoring goals, he could go to even bigger clubs, like Steven Fletcher did.
"He showed he could score goals at that level and has gone on to bigger clubs since he's been down there."