World Cup hooker Huw Bennett looks likely to miss Wales' bid for Triple Crown glory against England at Twickenham on Saturday.
Wales assistant coach Rob Howley has revealed Ospreys forward Bennett, who won his 50th cap in the victory over Ireland earlier this month, is struggling to recover from injury.
But Wales are hopeful other players with knocks, including star wing George North and skipper Sam Warburton, will be fit and available to face their unbeaten RBS 6 Nations title rivals.
Former Wales captain Matthew Rees, who missed the World Cup due to a neck problem, is favourite to replace Bennett if he shakes off a calf muscle strain that sidelined him against Ireland and Scotland earlier this month.
"It looks as if Huw Bennett is unlikely to make it." Howley said.
"Richard Hibbard has been brought into the squad, and Matthew Rees will train today. The medics are very hopeful, and we will know more about him in the next 24 hours.
"George North (ankle) seems fine. He has come through rehab well, without doing too much, and we hope he will start on the weekend."
Like Rees, Bennett has calf muscle trouble, and Wales coach Warren Gatland will want to keep changes to a minimum as he assesses his options ahead of Tuesday's scheduled team announcement.
Warburton's back-row return instead of Aaron Shingler, and Rees instead of Bennett could prove to be the only switches as Wales target only a second Twickenham success since 1988.