Menzel, 27, became a Swan after the club picked him up as a delisted free agent as the forward failed to secure a new contract with Geelong.
Lyon told SEN Breakfast he is concerned about the total net profit when it comes to Menzel.
“It’s not the two goals, it’s the net result,” Lyon said.
“The discussion about his defensive forward work stuff and the fact he doesn’t tackle and put a lot of pressure on, results in goals the other way.
“He might be kicking two goals, but it’s the net result that Geelong have looked at I’m sure and why other clubs weren’t that keen.
“If he kicks 40, then I reckon he could also cost 40.”
Menzel has played just 73 games in six seasons for Geelong, due to needing four knee reconstructions, where he has kicked 136 goals for the Cats.
Former Essendon captain Tim Watson believes Menzel will find himself out of the team if he cant put out a defensive forward effort worthy of keeping him in the side.
“Given historically the way Sydney play, he won’t be in that team if he can’t do what they want him to do,” Watson said.
“Even though they’ve recruited him and they’ve only given him a one-year deal, if he doesn’t do what they want him to do, they just won’t play him.
“And they’ve shown that in the past – you either step up or play the Sydney way or you don’t play, they don’t carry blokes who just play on the outside and don’t participate in the defensive side of the game.”