Sale's 22-year-old tighthead has stepped into England's Six Nations squad, to offset injuries to British Lions scrum cornerstone Alex Corbisiero and Bath's David Wilson.
England boss Lancaster expects a calf injury to sideline Wilson until the third-round Six Nations clash with Ireland, on February 22.
Leicester's teak-tough tighthead Dan Cole will be England's frontline number three for trips to France and Scotland.
And Lancaster has conceded Sale's highly-rated but extremely green two-cap prop Thomas must make big strides, and fast, before the Six Nations kicks off next month.
"Losing Davey Wilson is a big blow," said Lancaster.
"He will probably be fit for the third Six Nations game, the Ireland game.
"But Henry Thomas has spent a lot of time with us in camp a nd this is his opportunity now to prove he's ready for international rugby.
"Beyond there (Harlequins') Will Collier is the next in line. He's still relatively inexperienced himself.
"There's no doubt about it, we need to develop more experience in the tighthead position."
Quins prop Paul Doran-Jones has six England caps but has been out of the reckoning for some time, as have sometime Saxons Gloucester duo Rupert Harden and Shaun Knight.
Lancaster remains confident Thomas can handle the pressure of clambering off the bench into the final quarter against France's gnarled and wily scrum at the Stade de France.
"I think Henry will be alright," said Lancaster.
"When you put him alongside Dylan Hartley, Tom Youngs and with the likes of Joe Launchbury and Dave Attwood behind him, and then with someone like Tom Wood on the flank as well, he'll have a lot of experience around him."
Lancaster has jettisoned France-bound Toby Flood in favour of promoting 20-year-old George Ford to the full Elite Player Squad.
Flood will leave Leicester for Toulouse in the summer, effectively ending his international career at 60 caps as England do not select overseas-based stars.
In-form Ford will compete with first-choice Owen Farrell and Gloucester's off-kilter Freddie Burns, with Northampton's Stephen Myler joining the senior squad for training.
Burns' form has dipped out of sight as he agonised over renewing his contract with Gloucester before deciding to move to Leicester in the summer to replace Flood.
Burns will play at home ground Kingsholm in England Saxons' clash with Ireland Wolfhounds on January 25 and Lancaster said: "Most players go through a bit of a dip in form at some point and he's not really played in the last couple of weeks.
"That's the reason why I want him to play in the Saxons game. H e's not really had that much international rugby yet, so it's a great chance for him.
"We can see the quality in him, and we're confident that he and Gloucester will improve.
"I wouldn't say it's a technical issue he's had, clearly what's gone on off the field has affected his performance on the field a nd I think he needs to put that to bed and concentrate on playing well.
"Part of that is running a game well, defending well.
"We know he can do it in attack but clearly his goal-kicking, as well, will need to get back up to where it was, which was 65 to 70 per cent plus."
Danny Cipriani is another talented fly-half yet to realise his international potential.
Lancaster acknowledged the 26-year-old's improving form at Sale, revealing he called the former Wasps star to let him know he had not made the international cut.
Challenging Cipriani to force his way onto England's summer tour to New Zealand, Lancaster said: "I had a long conversation with him on Wednesday, a good chat; I have watched all his games.
"He's been a lot more consistent this season b ut I want to leave him at Sale to keep making progress, which he accepted and he said he felt it was the right thing to do.
"I've said to him his goal has to be to get onto that New Zealand tour.
"There's certainly no issue with him as a person. There are some areas where he's got some ground to make up as we move towards the World Cup.
"He's beginning to make up that ground though, which is good."