Ireland scrum-half Eoin Reddan is unlikely to take part in Saturday's clash with Scotland in Dublin due to injury.
Reddan sustained a calf injury during training on Wednesday and his place in Ireland's 34-man squad has been taken by his Leinster team-mate Isaac Boss.
Boss' call-up is a just reward after he won the man-of-the-match award in the Irish Wolfhounds' victory over England Saxons at Kingsholm last weekend.
"We've called Isaac in for the session this morning because Eoin has a slight problem with his calf," said Ireland's assistant coach Les Kiss.
"We'll give him until the end of the week and see what happens. It's very unlikely that he's going to be there.
"Bossy had a sensational game against the Saxons. So he is ready to step up if required."
Meanwhile, second row Mike McCarthy is also battling to be fit. McCarthy received 23 stitches to a head wound following a stamping incident in Leinster's Round six Heineken Cup match against the Ospreys.
Kiss believes McCarthy will be able to play, if selected, as much of the swelling to the wound has subsided.
"When you saw him the first week it didn't look nice," added Kiss.
"His face had swelled up. But it's come down a lot. He has to wear gear to protect it so there are some issues around it although it wouldn't stop him from playing."