Ireland coach Joe Schmidt has hinted that veteran centre Gordon D'Arcy's World Cup berth could be under threat.
Ian Madigan performed solidly at fly-half to move a step closer to securing his World Cup spot as Ireland scored four tries in beating Scotland 28-22.
D'Arcy struggled to impose any authority at inside centre however, with Schmidt insisting he does not need two out-and-out 12s in his final 31.
"We haven't put any rigidity around those decisions," said the head coach.
"I think we're reasonably open-minded apart from thinking we'll have a 17-14 split between forwards and backs," explained Schmidt, who will name his World Cup squad on 31 August.
"How we split that up will be defined by who fits where, and certainly in the backs we're reasonably open-minded about who fits where."
|Ireland's remaining World Cup warm-up games|
|Wales (home)||Saturday 29 August|
|England (away)||Saturday 5 September|
Remaining "open-minded" about his backline carve-up could mean bad news for 35-year-old D'Arcy, who made his first Test appearance since last November in Dublin on Saturday.
Madigan's versatility to cover fly-half and centre, not to mention full-back, could open Schmidt's selection options elsewhere - and D'Arcy could take the full impact.
Robbie Henshaw will start at 12 for Ireland with Johnny Sexton at fly-half, fitness permitting, so Madigan's ability to deputise for both adds an extra card to Schmidt's selection deck.
Ireland's Kiwi boss admitted in midweek that versatility will go a long way to forcing the selection issue.
The Ireland boss was pleased with Madigan's offering at fly-half, especially in teeing up tries for Zebo and Fitzgerald.
"I think he demonstrated that he can play the position," said Schmidt of Madigan as a fly-half.
"His line-kicking was spot-on, his kicking off the tee was super and his pass delivery was very positive.
"There were two crucial involvements in the lead-up to the third try and the crucial involvement in the lead up to the fourth try.
"He'll be reasonably tough on himself and look for more, and he'll have some ideas about what he can do better."
Should D'Arcy's bid for a fifth World Cup campaign fall by the wayside, the 82-cap centre will return to Leinster to boost provincial resources during the tournament, and then retire before Christmas.
Ireland now face a fallow week after two World Cup warm-up victories, where Schmidt admits he will sit down with his fellow coaches for lengthy selection meetings.
Ireland will still face Wales in Dublin and England at Twickenham before launching their World Cup challenge in Pool D against Canada in Cardiff on Saturday, September 19.