The Essendon speedster was caught biting the neck of Bulldog Tory Dickson during their round three clash last weekend and was sent straight to the tribunal.
He plead guilty to the charge which knocked his suspension from four weeks down to three but Murphy says he should have gotten five.
“Three weeks is not enough,” he told SEN Breakfast.
“I can’t get my head around the fact that we have a game at the moment where you can get two-to-three weeks for a sling tackle, and then the same punishment for someone biting someone on the neck.
“If you have been found guilty of biting, four I would have been okay with, but I had it at five.”
Appearing on behalf of the AFL, Jeff Gleeson said at the tribunal that the incident was “not in the spirit of the game.”
“It is rather inexplicable, a quick scuffle resulting in a bite,’’ he said.
“This was a bite to the neck. He moved towards a part of the body which is particularly vulnerable and he bit the neck.
“In no game, in any era, has biting been an act in the game.”
McKenna will now be next available for selection ahead of round seven.