"At the end of his contract a player is in a position of choice. We have to respect Forster's choice and wish him all the best," the Royals boss told the clubs official website.
"In a way we were expecting this to be the case, and it won't change our thinking in terms of transfers because we've always been looking at who is available.
"Forster has been an integral part of this club for a number of years and I'd like to thank him for all his efforts."
Stoke City and Sheffield United are rumoured to be interested in signing Forster.