Despite celebrating his 36th birthday earlier this month Williams was hoping for a possible late call up for a fourth World Cup with Wales if there were any injury problems in the back row. He is one cap short of reaching 100 for his country, although he also has five British &Irish Lions Tests to his credit.
One of the stalwarts of European rugby, Williams made his Heineken Cup debut for Pontypridd against Benetton Treviso way back in 1996 and was named as the first winner of the ERC European Fair Play Award in Paris last year.
He helped the Blues win the Amlin Challenge Cup in 2010 and is currently the eighth most capped player in Heineken Cup history with 80 appearances, 79 in the starting line-up.
The Blues are joined by Racing Metro '92, Edinburgh and London Irish in Pool 21 of this season's tournament. Their other No 7 is the current Wales World Cup captain Sam Warburton.
Heineken Cup Most Appearances
99 - John Hayes (Munster)
97 - Ronan O'Gara (Munster)
90 - Peter Stringer (Munster)
87 - Shane Horgan (Leinster)
86 - Anthony Foley (Munster)
85 - David Wallace (Munster)
81 - Fabien Pelous (Dax 5, Toulouse 76)
80 - Martyn Williams (Cardiff Blues 63, Pontypridd 17)