Newport Gwent Dragons prop Rhys Thomas and outside-half Craig Warlow look likely to miss the rest of the season.
Thomas won his first Wales cap in Argentina last summer
Tight-head Thomas, 24, who won his first Wales cap against Argentina in the summer, has a chest problem and must rest for an extended period.
He played the first six games of the season, his last match on 7 October.
Warlow has discovered that he broke a foot in the Dragons' last game, against Edinburgh on 11 November, and he will be in plaster until February.
Rhys is a big loss to us and we're trying to cover that by bringing a player in
Dragons coach Paul Turner
Ceri Sweeney and Mike Hercus can cover Warlow at 10, but the Dragons are short at tight-head with only summer signing Lee Harrison and teenager Jamie Corsi.
"Rhys is a big loss to us and we're trying to cover that by bringing a player in," Dragons coach Paul Turner told the South Wales Argus.
"We're looking at the situation closely in the build-up to two important European Challenge Cup matches against Bucuresti."
Back-rower Joe Bearman's ongoing hip problem also continues to be a source of concern to the Dragons, his participation against Bucuresti already in doubt.