The 35-year-old is in the Celtic Crusaders squad to face Harlequins two weeks after his debut in the 13-man version of the sport.
Thomas, who switched codes having had no prior experience of League, came off injured after just half an hour of his debut against the Catalans Dragons on March 19.
He missed the narrow defeat at Castleford last time out but is expected to be a big pull for supporters as the Crusaders take tonight's game to The Knoll, home of Rugby Union side Neath.
Having received the honour of captaining the Lions after taking over from the injured Brian O'Driscoll in 2005, Thomas went on to become the first Welshmen to win a century of caps for his country.
His record in the 15-a-side game is nothing short of extraordinary but, after just a limited number of training sessions with the Crusaders, he admits he is already wishing he had switched sports sooner.
"I remember talking to Kevin Ellis before I came up (to Wrexham)," Thomas told Sky Sports.
"And he said to me that you'll think to yourself that after a couple of weeks of playing it, you'll ask yourself why you didn't do it earlier. I was asking that question to myself after just two weeks of training!
"It's something so different and testing for me that I wish I was just had a few more years ahead of me to establish myself as it's a great game to play.
"The fitness levels are very different. Rugby League players are a lot fitter as it's a constant game, it's always on the go, you're always having to move back 10 metres.
"In rugby union, playing as a back, you have time to rest with scrums and line-outs and let the forwards do the work, but in league it's pretty much a team-game and everybody's working constantly.
"As Dylan Thomas said 'Ambition is Critical' and I feel fresh, I feel great and the first two weeks of training made me feel like an 18-year old again.
"I love rugby, the sport, the people, the fact I can run out onto the field in front of fans, and I don't want to lose that. I love challenges and there's been no bigger challenge for me than this one with the Crusaders now."