On Saturday evening, City got back to winning ways with a 3-1 victory over the Magpies at the Etihad Stadium, but Benitez was unhappy with a spot kick that was given for a foul on Raheem Sterling at 1-0 to the home side.
However, Gallagher has insisted that there was enough contact for the referee to give a foul against Javier Manquillo just after the hour mark.
Gallagher told Sky Sports News: "I think it is a foul because he decides to try and pull him, he can't pull him, and then he decides to push him.
"I think he does enough to bundle him over and it is a foul."
The result has left Newcastle sitting just one point above the Premier League relegation zone.