Ireland centre Robbie Henshaw is expected to be unavailable until at least the semi-finals of the Rugby World Cup due to a hamstring injury.
The Leinster centre sustained the issue in training this week, ruling him out of Saturday evening’s pivotal Pool B clash with Scotland in Paris.
Ireland will monitor Henshaw’s fitness for the time being but head coach Andy Farrell is weighing up his options and could eventually make a change to his 33-man squad.
“He pulled up with a hamstring unfortunately at the end of the session on Tuesday and the diagnosis with hamstrings, they want to see how things settle down,” said Farrell.
“It probably takes about five days for that type of thing to happen but it looks like it could be a minimum of a couple of weeks at this stage.”
Asked if Henshaw will remain in France, Farrell replied: “Obviously, we’ll assess that as we go.
“Certainly he’ll be around rehabbing and we’ll see how the weekend goes with other injuries, etc, and assess how Robbie’s going along the way also.”
Vice-captain Ryan suffered a wrist injury in Ireland’s 13-8 success over South Africa a fortnight ago.
Farrell insists the Leinster second row is fully fit and has trained well, including coming close to flattening captain Johnny Sexton on more than one occasion.
“He’s fit,” Farrell said of Ryan.
“He actually nearly took Johnny’s head off three or four times so he’s fit and raring to go, there’s no doubt.”
Ireland will progress to the knockout stages with a win or draw, while a defeat will leave them reliant on Scotland’s margin of victory and bonus points gained.
Farrell suggested the recalled Henderson, who came off the bench in the victories over Romania, Tonga and the Springboks, could be handy in calculating the permutations.
“But to the travelling fans and the people back home it’s a huge game.
“We have Iain Henderson in our group who is good at maths, so we’re across everything as far as that’s concerned.
“But the easiest way is to make sure that we perform well and deserve to win the game outright.”
Skipper Sexton will start for the fourth successive match following his return from injury and suspension at the beginning of the tournament, while flanker Peter O’Mahony will win his 100th Ireland cap.
“It is a knockout game,” said 38-year-old fly-half Sexton.
“We’ve viewed it as a last 16, we’ve spoken about it and that’s why it’s important we got our preparation right.
“We need to go out and get our performance right now.”