Peter Latchford - who played nearly 200 games for the Hoops in a 12-year spell and now works with Celtic's kid keepers at Lennoxtown - fears Forster may reject Celtic after being overlooked by England coach Roy Hodgson.
The 59-year-old told the Daily Record: "I can just imagine Neil Lennon jumping up and down going potty because Fraser has been offered a contract he hasn't signed yet.
"Fraser could be saying, 'If I want into this England side I've got to go and play in England'.
"That kind of thinking must drive Lenny bonkers because he could lose Fraser on that basis and nothing to do with the terms on offer.
"Fraser may feel he has no chance with England while in the SPL. He'll have to plug away and his chance might come but I hope he doesn't feel he has to go down south to get an international call because Celtic will lose a good keeper.
"The same happened with Alan Thompson and Chris Sutton when they were playing out of their skins against some of the best in Europe.
That was proof of how the SPL is dismissed in England.
"Fraser has done a great job here so justifiably he'll be annoyed."