Ferguson was furious with Cole's X-rated challenge on Javier Hernandez.
But Merson wrote in his column for the Daily Star: "He was wrong.
"Javier Hernandez got injured after Cole made that tackle on him - and Fergie called him reckless. I don't think he is at all.
"He is a top, top player, Ashley Cole. He wasn't out to injure the guy. For me he's going for the ball.
"You don't go out to hurt a player in your own box because it's a penalty. I don't understand all this stuff about the ball being out of play.
"That's the reason the ref gave for not giving the penalty. But that's rubbish, isn't it? It should have been a penalty.
"I think Fergie was angry because he's lost a player - and he's entitled to his opinion. But he was wrong to accuse Ashley like that."