Wales have suffered a major Six Nations blow after Bath number eight Taulupe Faletau broke his arm for the second time this season.
Faletau is not among Wales head coach Warren Gatland's 39-man squad, but full-back Leigh Halfpenny has been included.
Gatland confirmed that he had originally selected a 40-player group, which included Faletau, before injury ruled him out.
Faletau returned to action for his club Bath against Heineken Champions Cup opponents Wasps on Saturday.
That was the 28-year-old's first appearance following a 13-week absence after he broke his arm earlier this term, missing Wales' four autumn Tests as a result.
And Bath have now confirmed another fracture to the same arm, although no timescale has been given for how long he will be sidelined.
Scarlets star Halfpenny, meanwhile, has not played since suffering concussion during Wales' victory over Australia on November 10.
Scarlets head coach Wayne Pivac stated last Tuesday that the 30-year-old would not feature for "three to five weeks" after seeing a specialist.
That would suggest he will be unavailable for Wales' Six Nations opener against France on February 1, which is followed by an appointment with Italy in Rome eight days later.
Halfpenny went off in the closing stages of the Australia match after being on the receiving end of a late challenge from Wallabies centre Samu Kerevi, who avoided any punishment.
Gatland's Six Nations group includes Wasps flanker Thomas Young and Leicester back Jonah Holmes.
Young, who won caps against Tonga and Samoa in 2017, has been among the Gallagher Premiership's form players this term.
Holmes made his Test debut earlier this season, and he has continued to shine for his club Leicester, despite the Tigers' inconsistent form.
Lock Alun Wyn Jones captains a squad that features many of Gatland's tried-and-tested players, including fit-again Cardiff Blues back-row forward Josh Navidi, who mussed the autumn games through injury.
This season's tournament is Gatland's final Six Nations as Wales boss. He steps down after the World Cup in Japan later this year.
Gatland said: "We have a really experienced squad of players who have been around a number of campaigns together, and we feel we are in a pretty good place going into this huge year.
"We have got a few injuries and have selected a larger squad because of that."
Wales squad for the Guinness Six Nations:
Backs: A Davies (Ospreys), G Davies (Scarlets), T Williams (Cardiff Blues), G Anscombe (Cardiff Blues), D Biggar (Northampton), J Evans (Cardiff Blues), R Patchell (Scarlets), J Davies (Scarlets), H Parkes (Scarlets), O Watkin (Ospreys), S Williams (Ospreys), J Adams (Worcester), H Amos (Dragons), S Evans (Scarlets), L Halfpenny (Scarlets), J Holmes (Leicester), G North (Ospreys), L Williams (Saracens).
Forwards: R Evans (Scarlets), W Jones (Scarlets), N Smith (Ospreys), L Brown (Dragons), T Francis (Exeter), S Lee (Scarlets), D Lewis (Cardiff Blues), E Dee (Dragons), R Elias (Scarlets), K Owens (Scarlets), J Ball (Scarlets), A Beard (Ospreys), S Davies (Cardiff Blues), C Hill (Dragons), A W Jones (Ospreys, capt), R Moriarty (Dragons), J Navidi (Cardiff Blues), J Tipuric (Ospreys), J Turnbull (Cardiff Blues), A Wainwright (Dragons), T Young (Wasps).