Henson, making a first appearance for his country since the Six Nations finale against Ireland in 2009, looked understandably rusty in the defeat to the Baa-Baas as he tries to adjust to being back at the game's highest level, although he did create Wales' opening try for wing George North with a wide, and suspiciously forward, pass.
The 29-year-old was then named in Wales coach Warren Gatland's preliminary 45-man squad for the World Cup in New Zealand in the immediate aftermath of Saturday's contest.
And Johnson believes Henson can eventually reproduce the form that made him an integral part of the Grand Slam-winning sides of 2005 and 2008 as he looks to be involved in the game's global showpiece for the first time.
Former Wales caretaker coach Johnson, who was Henson's boss at the Ospreys until the wantaway star headed to Saracens earlier this season, said: "To be fair he hasn't played a lot. It's not the Gavin of old, I think that's clear to see, but it doesn't mean he can't get back there.
"He has played limited rugby and it showed in some cases, but he is a quality player and he has a bit of time in his favour, but that's for someone else to worry about now."
Henson, who is without a club after Toulon opted not to offer him a new contract at the end of the season, had hinted through the media he would be interested in a return to the Ospreys.
But Johnson said: "I have not given it a thought since I came into camp (with the Barbarians) two weeks ago."
Henson was also linked with the Cardiff Blues during the week, but Blues boss and Baa-Baas head coach Dai Young dismissed any talk of a move for the 2005 Lions tourist as "pure speculation".
"I said in the week that I was flabbergasted as no-one knows where the link came from," he said.
"It's easy to say it's come from sources, but what does that mean?
"From a coaching perspective you get annoyed when things are written with no foundation. Everyone knows where the Blues are. We have a strong squad but are not looking to bring anyone in. It's is purely media speculation."
Henson himself had admitted he had not been at his best as Wales suffered a fifth home defeat of the season thanks to a brilliant last-gasp Barbarians try from Leinster full-back Isa Nacewa.
He told BBC Wales: "I am very proud, getting back into that Welsh jersey.
"I have really enjoyed the week, getting back in and playing.
"But I am bitterly disappointed with my performance, there were some bad decisions I made.
"It was a good game to be involved in and it was a pity we lost in the end."
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