The move is a little surprising as before Merson moved to Walsall, Megson ruled himself out of a move for the player because he didn't want the baggage!
It is believed that Megson sees Merson as the short term solution to bring experience into the squad.
Upon Mersons release from Walsall i presumed he would drop a level or 2 where his footballing brain would compensate for his lack of fitness.
Merson would probably be very interested in a move to a club the size of Nottingham Forest, especially as its a short commute from his Sutton Coldfield home.