Cory Allen was carried off on a stretcher off as Leinster beat Cardiff Blues 14-13 in the Pro 12, increasing Wales' Six Nations injury worries.
Warren Gatland's men are already without Scarlets' Scott Williams as he battles a knee problem, while Jonathan Davies is in doubt for the crunch match against France next Friday after missing Clermont Auvergne's Top 14 win over Castres on Saturday due to a groin issue.
And now another centre is under an injury cloud, Allen having turned his ankle early in the second half of the narrow loss at Cardiff Arms Park.
The 23-year-old will wear a protective boot for the next 24 hours before undergoing an assessment, according to Blues coach Danny Wilson.
Isa Nacewa's try and the boot of Ian Madigan, who sent over three penalties, sealed the points for Leinster.
Blues narrowly failed to snatch the win right at the death, Rhys Patchell missing an 81st-minute drop goal attempt after converting Josh Navidi's try to get the hosts back to within one point.
In the other match on Saturday, Connacht moved two points clear at the top after a thumping 51-34 win at Zebre.
Matt Healy enjoyed a hat-trick of tries, Niyi Adeolokun had a brace and Kieran Marmion crossed for the other, Alan MacGinty and Craig Ronaldson converting three apiece and notching three penalties between them in the crushing victory at Stadio Lanfranchi.
Zebre were seeking to respond to their second biggest Pro 12 defeat, a 52-0 loss to Leinster last time out.
And while tries from Johannes Meyer, Dries van Schalkwyk and Federico Ruzza kept the scoreboard ticking over in this one, the second-bottom Italian side proved unable to cope with an onslaught from Irish opposition for the second match in succession.