Johnson was taken ill just before the Ospreys' vital Magners League win over the Scarlets on April 2 and missed the away trips to Ulster and Leinster as a result.
There had been fears that he may have been forced to watch tonight's match in front of a television back home in South Wales but Johnson will instead be pitchside at the RDS as the Ospreys go looking for a third Celtic crown.
"Scott's fine," said fellow Ospreys coach Sean Holley.
"He was a bit dizzy on the flight but he's managed to come over.
"He obviously hasn't been too well recently but he's on the men and on an upward curve.
"We're delighted that he'll be floating around the touchline."
Johnson himself recently told the media that, while he isn't yet fully back to his usual energetic self, he wouldn't be letting the illness stand in his way of the Ospreys' charge towards Magners League glory.
"I'm not 100%, not where I want to be but certainly much better than I was a few weeks ago," said Johnson.
"I'm up on my feet doing as much as I can with people around me.
"But when you're at this level and late in the year, you probably do less anyway.
"I came down with something and I wasn't sure what it was as I don't get sick a lot. It certainly took me by surprise.
"I took ill the week before the Biarritz match. Probably one of the dumbest things I did was fly to Biarritz. What really killed me was the flight - I've certainly paid for it since."
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