Off-field controversies, injury, suspension and a loss of form over the last 20 months have all combined to keep Henson from fulfilling his true potential.
But Johnson, a key figure in Henson's development to the point where he peaked in Wales' 2004 autumn series, knows exactly what the Ospreys centre is capable of and Australia have been fully briefed.
"Gav has always had issues off the pitch. He is high profile and with that comes a responsibility and it is hard work," said Johnson.
"He is a talented kid and I have the utmost respect for him.
"He can do things that not a lot of people can do. That is a talent you like to have on your team and, given his chance, I am sure he will do well.
"It is up to us to make sure that doesn't happen."
Henson will slot into a familiar back division alongside fly-half Stephen Jones - his new captain - and centre partner Tom Shanklin.
Australia, on the other hand, are experimenting and the task of keeping Henson quiet will fall largely to Stephen Larkham, who has been named at inside centre for the first time in his 92-Test career.
Larkham has played all his international rugby at full-back and, for most of the last decade, fly-half.
Johnson's influence on the decision is clear. While working as the Wales skills coach, he did exactly the same with Henson.
Defensive re-alignment is the biggest problem Larkham faces this weekend and it is an area Wales could look to exploit.
Larkham said: "In attack, the change is giving me a little bit more time with the ball, a bit more width but defensively is going to be the hardest role for me.
"Gavin's a very skilful player, he's got a very big boot on him, he's a very good runner of the ball and some good passing skills, a pretty complete all-round player and someone that we're certainly going to keep an eye on and mark closely when we get out there."
Australia's shock defeat to the Ospreys on Wednesday night was a wake-up call for the Wallabies Test squad.
The defeat has been described as the worst in Australian rugby history and Larkham said: "Everyone's disappointed, not only with the result but with some of the passages of play that we put together, so it's not necessarily a bad thing that we started the tour with a loss.
"I think it has put us in the right frame of mind and we all realise that football over here is different and a lot harder than we probably thought it would be."