The midfielder was subject to a £1million bid from Bristol City last week but turned down the move.
Looking to strengthen their hold on the player against the possibility of future interest, the Whites negotiated an extra two years on his contract.
Thomason will be part of the squad facing Fleetwood Town tonight and Ian Evatt hopes he can be a big player for Wanderers this season as they look to beat a path to the Championship themselves.
“I think it is an illustration of the progress the club has made,” he said. “I think George can take great credit and heart that someone from the league above tried to acquire his services for a significant amount of money. That is a line in the sand as to where he is right now – he is a young player who has a huge amount of talent, who can do a lot of things and ticks a lot of boxes for a midfield player and being only 22 I think he has got a huge amount of improvement to come, a real high ceiling.
“The best and biggest thing I can say aside from his footballing ability is his character. He is a very special young man and his family have done a pretty good job with him, I have got to say.”
Wanderers have made a fast start to the season, winning their first three games in league and cup, but their early form has not been a great surprise to Evatt, who felt in the summer that his players had stepped up a level.
“It is part of our evolution,” he said. “We have to remember we did quite a bit of business in January and sometimes getting the best out of those players can take time. We’d always spoken about that full pre-season, and I have seen vast improvement from all of our January recruits.
“The ones we brought in this summer have had a good start too – Nathan Baxter, Josh Dacres-Cogley, we have Paris Maghoma, Carlos Mendes Gomes and Dan Nlundulu who are constantly working hard, striving to get into the team and getting used to what we do.
“I think we are in a pretty good place.”