Wales squad centre Cory Allen was due to undergo a scan on Monday after being injured during Cardiff Blues' Guinness PRO12 clash against Leinster.
Allen was carried off after suffering an ankle injury, and Wales assistant coach Rob Howley told reporters that Allen faces further assessment to "determine the extent" of his injury.
"We are hopeful it won't be as bad as first thought," said Howley, who was speaking at Wales' training base ahead of Friday's RBS 6 Nations clash against France in Cardiff.
"He is due to have x-rays and scans to determine the extent of the injury. It's unfortunately the nature of the weekend between Six Nations games. It's the same for every other country. It's a difficult time.
"You are hoping and praying that the players released don't get injuries. Unfortunately, with Cory, we have come up a little bit short."
Centre Jonathan Davies, meanwhile, was due to train on Monday afternoon. Davies missed his French club Clermont Auvergne's league game against Castres two days ago due to a groin problem.
Davies, who is an integral part of Wales' Six Nations title ambitions, recently returned to Test rugby after missing the entire World Cup earlier this season because of a serious knee injury.
And Howley said that lock Luke Charteris was continuing his rehabilitation with Wales' medical staff. Charteris was not involved for Racing 92 in their French Top 14 appointment with Grenoble on Saturday due to knee trouble.
But fly-half Rhys Priestland was in training on Monday, albeit non-contact, after suffering what Howley described as a "dead leg" during Bath's Aviva Premiership home defeat against Wasps.