The British & Irish Lions tourist picked up mumps last week and has been unable to train properly for the past 10 days, leaving Leinster coach Michael Cheika with no option other than to leave him on the sidelines.
"Rob's not going to make it. Even if he was to get himself out on the field he has had no training behind him for the last 10 days, so we wouldn't even consider it," said Cheika.
"He had to go to hospital because he had quite a high fever, but he's ok now. He has recovered well and the doctors have really looked after him well and he's in good spirits too.
"The priority for him is to become healthy again and for us to get him back on the field as soon as we can. It's times like this that you're happy to have the kind of squad that we have with top quality players."
Another 2009 Lions tourist, Luke Fitzgerald is among the candidates to take over the No 15 jersey for the 'Battle of Ireland', although it is likely that he will remain on the wing with the veteran Girvan Dempsey coming into the back line.