Full-back Leigh Halfpenny has been ruled out of Wales’ Guinness Six Nations opener against Ireland in Cardiff on Saturday.

Halfpenny was due to win his 98th cap and make a first Wales start for 19 months, but assistant coach Jonathan Humphreys said he had suffered a back spasm and would miss the game.

Experienced Cardiff back Liam Williams will replace Halfpenny in the number 15 shirt, joining Dragons winger Rio Dyer and Josh Adams in the back three, while Dan Biggar will have kicking duties from the tee.

Williams missed Wales’ entire Autumn Nations Series campaign this season because of injury, and has not started for his country since last summer’s South Africa tour.

Halfpenny made featured against Georgia as a replacement but the 34-year-old pulled out of the sides to face both New Zealand and Australia after initially being selected.

Humphreys said: “Unfortunately, Leigh had a back spasm this morning and Liam will be playing.

“I think it’s more disappointing for him as a person. He is an unbelievable professional and an unbelievable person.

“He has got to pick himself up again. You feel for him that he’s got to pull out at this late stage. Liam is good to go.”