The former official casts his eye over the big calls made by Mike Dean at Carrow Road on Saturday.
The two relegation battlers were level at 2-2 going into injury time of the pivotal clash at Carrow Road when Martin Olsson fired home to break Magpies hearts and make their situation at the bottom of the table far more serious.
There was some debate after the match as to whether the winner should have stood with the manner in which Canaries midfielder Jonny Howson controlled the ball in the build-up to the goal.
Gallagher, who refereed for 15 years in the Premier League before retiring in 2007, has claimed that Newcastle were denied a valuable point as the goal should have been ruled out for a handball by the former Leeds United midfielder.
The 58-year-old told Sky Sports: "[The] goal should be disallowed. On Saturday I was watching this game live and I called handball straight away.
"I was sat next to another former referee who said no. The referee has got the best view and he thought no. That's where we're sat. We're not sure. There needs to be a sit-down to say, 'This is handball, this is not handball. This is why, this is why not.'"
Gallagher also discussed the handball call that was given just five minutes earlier, when the ball clearly struck the arm of Norwich's Gary O'Neil and referee Mike Dean awarded a spot-kick, which Aleksandar Mitrovic converted to level the score at 2-2.
The ex-referee said: "Penalty. This was almost a panic reaction, he sees the ball there and his arm is up. He moves his arm through and I can understand why the referee gave that."
Olsson's late winner had a huge effect on both clubs with only a handful of games remaining before the end of the season, and it has done a significant amount of damage to Newcastle's survival bid.
The 3-2 defeat leaves Rafael Benitez's side six points adrift of safety with only seven matches remaining, although they do still hold a potentially crucial game in hand over the Canaries.