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The 31-year-old Ospreys wing, scorer of 45 tries in 62 Tests, has failed to recover in time from an ankle injury suffered during the 26-13 victory over Scotland last weekend.
Scarlets winger Mark Jones will win his 44th cap as Williams replacement. In the only other change to the side which began its defence of the Six Nations title with a convincing 26-13 win over Scotland last weekend, Ryan Jones returns at blindside flnaker after missing the Murrayfield clash with a leg injury.
The only other injury doubt concerned Andy Powell but the Blues No8 passed a fitness check this afternoon to take his place in the back row.
