Usually a Manchester United goalkeeper is only replaced if he is injured or 'having a Massimo Taibi', so Sergio Romero must have been perplexed when he saw his number go up.
Joel Pereira, a name probably not familiar to many, came on his place. Romero was not injured and United had not conceded a goal. It was one of those changes that raised eyebrows but as it had no impact on the course of the game was hardly quibbled.
Post-match Jose Mourinho offered such a simple explanation for the change as if it were an weekly occurrence.