Here, pay attention very closely.
If the player subbed off recovers, as happens many many times; rolled ankles, concussion, tight hamstrings and groins, broken finger, etc. and somebody else gets injured you are 2 players down with only 1 injured player. Therefore you only have 20 players to rotate against 21, therefore much suckage for you when it could be 21 v 21 still.
So if that's not worse off what is?
Suggests to me that the coaches stuffed up.