McClaren's reign marks the end of his bid to restore his reputation after being axed as England boss in 2007.
Forest legend Garry Birtles believes McClaren was right to quit.
Birtles, who won the European Cup with Forest in 1979 and 1980, said: "Steve was told something else when he had his job interview.
"There have been so many statements about ambition. If there's no money available, why didn't the chairman say?"
Kenny Burns, who is also a double European Cup winner, said: "People talk about Martin O'Neill coming but he won't now with no guarantees on money."