Clark, 68, who played for Forest in the 1970s, winning the Football League Championship and the European Cup, before managing the club between 1993/96, has succeeded Nigel Doughty who stood down 10 days ago but remains as owner.
Since retiring from management Clark has been vice-chairman of the LMA for over a decade. His first task will be to appoint a new manager to succeed McClaren, who resigned 11 days ago. Clark plans to use a decade of experience in dealing with managers to help Forest appoint the right man for the job.
"I know a lot of the managers through my role at the LMA and that could be beneficial. That is one of the areas that I felt I could help the football club," Clark said. "We've got to find a manager as quickly as possible, but hopefully not to the point of rushing it and making a mistake. We need to get it right as it is a very important time for the club.
"While I can understand the urgency, we just need to be careful and make sure that we get the best manager out there who is available. We need somebody who is enthusiastic and ambitious. We need someone who is prepared to spend a lot of time out on the training pitch with the players.
"We are not going to be a big-spending club in the transfer market so we need someone who can work with what he has already got, maybe with one or two additions hopefully. Preferably, we need someone with a bit of experience and some hunger to succeed in the game."
Clark added: "I will have to leave my role at the LMA. The two are not compatible unfortunately. So I will be resigning from the LMA committee and suspending my membership from the association."