Talking to BBC Radio Kent, Stimson said: "As a player he's got fantastic ability, but whether he's got the same commitment as I have and the desire I have, that'll be a different answer and unfortunately in the modern day it's not just about ability.
"The Ronaldos, the Wayne Rooneys, the Fabregas' the Steven Gerrards, they'll always use that phrase, 'work hard'.
"If Gary looks at himself and [is] honest, then is he working hard enough? I don't really know."