Ole Gunnar Solskjaer’s decision to field a back three against Liverpool last month worked a treat as the Reds kept the visitors’ threat to a minimum during the 1-1 draw, and we then started with Harry Maguire, Marcos Rojo and Phil Jones at the heart of the backline away at Partizan Belgrade before changing to a four in the second half.
The same alteration happened during Wednesday's superb Carabao Cup victory at Chelsea with Victor Lindelof, Maguire and Rojo setting up in a three, before Ole switched things around again late on.
Romero was in goal in Belgrade and at Stamford Bridge and says both systems allow the Reds to cause problems in different ways to the opposition.