Ospreys coach Lyn Jones says Henson is over the bout of food poisoning which ruled him out of contention ahead of their opening defeat by Cardiff Blues last Friday night.
And while Jones says Henson has worked "really hard" in training, the coach also warned not to expect too much too soon from the player who was controversially omitted from Wales' World Cup plans by Gareth Jenkins.
Jones said: "We are delighted Gav is ready to restart his career.
"He's obviously had a long time off and the recent bout of illness obviously didn't help.
"He's really worked hard and diligently and I can see him playing some part against the Scarlets.
"There is going to be a lot of expectation on Gavin on Tuesday, but I feel we need to keep our feet on the floor and understand this is his first game for us for a very long time.
"His last game for us was last January and he's never played for us since."
He continued: "When boys have been out of the game for a while, it takes a huge amount of time to get back to where you came from and there is no pressure on him.
"He either starts or comes off the bench and it's just important that he gets a little bit of time under his belt and starts building up to what Gavin can produce.
"He's been training and really worked hard. He's looking quite focused and quite excited at the prospect of getting back on to the field with the Ospreys.
"He had food poisoning - and anyone who's had food poisoning will realise that it really takes a bit of time to come back from it.
"What's important is that with the expectation on him, he is feeling 100% right and he now is." Henson made two cameo appearances for Wales as a replacement in their two-Test defeat in Australia in May and June, but suffered Jenkins' axe 10 days before the announcement of Wales' World Cup squad.
At the same time hip-injury victim Stephen Jones was included in the squad and Ospreys lock Ian Evans, who has not played since last December, remains in the tournament party despite not having played since December and with no solid news on his likely comeback date.