Sky Sports News pundit Gallagher telephoned referee Clattenburg following the controversial Stamford Bridge encounter to ask him why he had shown Torres a second yellow card for diving.
Clattenburg, accused by Chelsea of using "inappropriate language" towards two of their players in a separate incident, told Gallagher he felt the Spain forward had overrun the ball before going down after being challenged by United's Jonny Evans.
Gallagher said: "What Mark has said is he felt it was an over-exaggerated fall. It wasn't natural. He's tried to deceive him, to get a free-kick and Jonny Evans into trouble. Therefore in law 12 of the game he's well within his right to caution for a yellow card offence.
"Like everything in football it's subjective, he has his opinion. I thought it was a foul (but) I've seen it many, many times in replay and I've had a facilty to blow it up."
Gallagher added that he could not speculate on Chelsea's complaint of inappropriate language but revealed Clattenburg had impressed him enormously last season.
He said: "I thought the two best performances last season were in two of the Manchester derbies. Ironically Mark Clattenburg was referee when City won at United 6-1. I thought it was absolutely exceptional."