The hosts lost 2-1 despite dominating the match, and afterwards manager Neil Lennon pointed the finger of blame at referee Kevin Clancy to missing a handball by Rangers defender David Bates in the second half.
Gallagher, appearing on Sky Sports to give his take on the decision, agreed that it should have been a penalty. However, he gave reasons as to why Clancy, and his assistant referee, failed to make the call.
He said: “I think the fact he leans in and makes sure that he blocks the ball with his arm - it’s a penalty.
“The only mitigating circumstance is that the referee is on the other side of Bates. You look across at the assistant and say ‘can he help?’ But there are bodies in the way.
“When you look at it on the replays, it looks like an easy penalty to give. That’s the unfortunate thing about being a referee - you don’t always have that perfect position which makes it an easy decision.
“There are many times when you look back and think ‘if only I had been standing there’ instead, but in the natural flow of the play it’s not always possible.”