Defender 'Doc' - on the road to recovery from a broken leg - has played with Keane for Ireland since their days as Under-17 internationals.
Keane, back in action for Leeds in the UEFA Cup tonight, was a real handful for Manchester United last weekend and has forged a potentially dangerous partnership with Mark Viduka.
He has scored seven goals so far this term and Gary pointed out: "I've been playing with Robbie since I was 17 so even though I won't be playing, I do know his game.
""Robbie has so many assets. He's such a quick thinker, he's sharp in and around the box and you can't afford to give him a yard.
"He has so much ability. There is not much you can do because he is so off the cuff. He has a lot of class about him but the lads will know all about him."
David O'Leary's men top the Premiership with an unbeaten record after 10 games but Gary was positive about the trip to Elland Road.
"Let's be honest, they are flying and they have quality all over the place," he added. "It will be tough but the way we are playing at the moment I'd expect us to go there and get a draw."
Gary Doherty will not face his mate Robbie Keane on Sunday - but at least he can give his team-mates the inside track on how to stop Leeds' livewire striker.