It is a formation that Ole Gunnar Solskjaer is keen to bring in at United, in an attempt to utilise as many attacking players as possible.
But on the evidence of Wednesday’s win, such a formation change may fail to bring out the best in Fernandes and Ronaldo.
Ronaldo appeared to be moved out to the left wing for the second-half, though again Portugal struggled to penetrate the Irish backline.
The struggles reached such a point that Fernandes was substituted off just after the hour mark, to the visible frustration of the midfielder.
Though Ronaldo did win the game for the hosts, the match will prompt some doubt at United over the best way to utilise both Ronaldo and Fernandes in the same team.