But now the 28-year-old is fighting fit and in line to start against his ex-clubmates in an eagerly anticipated Welsh derby.
"I'm really excited about the prospect of going back to Rodney Parade," said Thomas, who was born and raised in South Africa but came through the ranks at Newport before spending six years with the Dragons.
"I would have loved to have done it last year but was injured for the fixture so this is my first chance to hopefully get stuck in and get a win.
"I will probably get a bit of stick. I still go down to Rodney Parade to watch some close mates play and I still live in Newport but I left on good terms. The stick might be a lot worse if we win but I will take it on my shoulders.
Thomas' first season at the Parc-Y-Scarlets was blighted by a toe problem that limited his Magners League appearances to just six starts and two games off the bench.
It was a massive disappointment for both Thomas and the West Wales region, particularly after his high-profile switch had been expected to stabilise the Scarlets scrum and heighten the player's international ambitions.
"Last year wasn't a great year for me, I was injured a lot," added Thomas.
"It was an unusual one because I ruptured the ligaments under my big toe in my right foot.
"My toe has a big bearing on being a prop because everything goes through your foot. I still have repercussions and struggle on a Monday after a game and have what they call turf toe.
"Last year, I was in a lot of pain, but it's better this year. I still have to do some pretty random exercises with elastic bands on my toes…but I am back now and I am really keen again.
"It's been an interesting pre-season and I have been able to put a lot of fitness in and it feels good.
"I feel I owe the Scarlets, they brought me down here and the first year was a disaster and I want to repay them. I also have a point to prove to myself too."