It was first feared Best’s injury, which he sustained in his side’s convincing win over Italy last weekend, would rule him out for this weekend’s all-northern hemisphere knock-out showdown but his AC joint on his right shoulder has responded to treatment better than expected.
Sean Cronin is on standby to start if the Ulster hooker fails to recover.
“We have to put a team in 48 hours before kick-off,” said head coach Declan Kidney. “The decision could go right to the end, we’ll make it when we have to make it. I wouldn’t want to tempt fate by rating Rory’s chances, but he’s not ruled out which is always the first sign.
“He had a good day yesterday which everyone was very positive about. He’s making great progress and we’re taking it one day at a time.”
Kidney brushed aside concerns that Wales will target Ronan O’Gara’s defensive frailties.
“They have quite an array of places where they can attack, I don’t think they’ll pick anyone in particular,” he said.
“Wales are a better side now because before you knew where they would attack, but now they attack other places too. It’s going to be a case of everyone defending their own zone.
“Playing Wales is a huge challenge. They got the better of us in March and are going well. They only lost to the kick of a ball against South Africa, otherwise they’d be on four wins from four games.
“They beat England and Argentina during the warm up games as well. They have a few younger players who have brought their own spark. The senior guys are showing good form too.
“They’re showing different trends in the way they play, but are more unpredictable than before. If it was possible to read them before, it’s more difficult now.”
Ireland: R Kearney (Leinster); T Bowe (Ospreys), B O’Driscoll (Leinster, capt), G D’Arcy (Leinster), K Earls (Munster); R O’Gara (Munster), C Murray (Munster); C Healy (Leinster), R Best (Ulster) or S Cronin (Leinster), M Ross (Leinster), D O’Callaghan (Munster), P O’Connell (Munster), S Ferris (Ulster), S O’Brien (Leinster), J Heaslip (Leinster).
Replacements: S Cronin (Leinster) or D Varley (Munster), T Court (Ulster), D Ryan (Munster), D Leamy (Munster), E Reddan (Leinster), J Sexton (Leinster), A Trimble (Ulster).