At the end of last season, Williams signed a one-year contract extension but a similar deal is not in the pipeline this season casting doubt on his playing future.
After missing out on selection for Wales, the 36-year-old played two matches for the Blues before breaking his arm against Ulster.
Williams though made a quicker-than-expected return to full fitness and played in the RaboDirect PRO12 clash with Connacht as well as the return fixture against Ulster which the Blues won 21-14.
But despite his iconic status in Wales after 137 appearances for the Blues and 99 caps for Wales, Thomas is adamant the club is in need of an overhaul and Williams will be one of a number of players not to get their deals renewed.
"There are a number of players who will be out of contract and their contracts won't be renewed," said Thomas.
"There will be a lot of players leaving but a lot of those players will have come to the end of their playing careers.
"The one classic example, and I'm sure he won't mind me saying so, is Martyn Williams."
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