NBC Won't Pull Plug on Jay Leno Prematurely

Jay Leno will be beached when his contract is up ... but not a day before -- this according to sources connected to NBC.

Jimmy Fallon will be replacing Jay on "The Tonight Show" when Jay's contract is up in September, 2014. There's been a buzz that NBC may not want to wait and will make the change before Jay's contract expires. Not gonna happen.

Informed sources connected with the network tell TMZ ... when Jay renegotiated his contract during the Conan O'Brien mess, he demanded and got several penalty clauses that would make NBC take an ENORMOUS financial hit if they pull the plug early.

We do not know specifically how much of a penalty NBC would have to pay, but we're told Jay made it so big, it would be too much for NBC to swallow.