Lee has suffered with ankle, Achilles and knee problems in recent seasons and Tomas Francis was preferred by Rob Howley in the Wales tighthead jersey in the 2017 Six Nations.
The powerful front rower also sat out the summer tour victories over Tonga and Samoa, but is now back fit.
Scarlets head coach Wayne Pivac says Lee is standing out in their pre-season campaign.
“Samson is full-on in training, he is making up for lost time and he has been impressive,” Pivac said.
“If you speak to any of the loosehead props who have been in training they will tell you he is a different machine at the moment.
“He is giving every loosehead a hard time. He is very determined, very motivated and clearly his objective is to get back that No 3 jersey for Wales, which bodes well for us.
“Certainly, he is over the knee injury and is very, very hungry to get out there and play.
“He has been brought forward a week and cleared to play against Bristol. He is wanting to play and he is putting his hand up and asking ‘how much game-time am I getting Wayne?’.
“He is raring to go, which is a good space for Samson.”
Lee is just 24, but already has 34 Wales caps to his name. Pivac revealed Lee’s injury suffered against Ireland at the 2015 World Cup has had a long-term impact.
“That injury was huge for him,” admitted Pivac. “It has taken a good 12 to 18 months just to get the calf muscle sizes the same, to repair the imbalance.
“It is one thing to repair the Achilles, but it is also about the muscle groups around it which struggled through that period of recovery.
“We gave him a six-week break when he came back from the Rugby World Cup, but really, he is only coming into his own now.
“With the break he has had and by not going on the Wales tour he is in a pretty good space at the moment. What is he? Twenty four? That is very young for the amount of experience he has got.
“I can see Samson having a fantastic career. If we can keep him injury free and have a good run of games, he will be better for that.”
Lee is set to feature for the Scarlets in their pre-season friendly at Bristol on Saturday.
“Samson’s skillset has improved over the last 12 months, we do a lot of work on his passing game, we do a lot of drills week in week out so we can play the style of game we want to play,” Pivac said.
“The forwards know they have got to be able to catch and pass under pressure. Now the focus is the set-piece to go with the round-the-park game. It is about getting the balance right in his game.
“I think Samson is going to have a big season.”
