While Arsenal’s three changes were made against Manchester City, Mikel Arteta was able to bring David Luiz into play to substitute of Rob Holding late in the game.

It is an image that has caused some questions at the end of the Premier League meeting between Arsenal and Manchester City this Sunday night in England.
While Mikel Arteta had already made his three changes in the second half,the Gunners coach was allowed to make a fourth. Why ?

Hit in the head after a shock to Joao Cancelo, Rob Holding left at the end of the meeting as a precaution, to avoid a risk of concussion or head trauma.
The FA Cup has allowed teams to make a fourth change in the event of brain danger to the player. Regardless of whether the three permitted changes in the Premier League have already been made, the player has the right to be substituted if the referee feels he has suffered a head shock.
This Sunday, Arsenal were the first team to benefit from this rule, and Holding gave way to David Luiz. And to prevent a team from being favored, the rules stipulate that the opposing team can also benefit from an additional change. Pep Guardiola could therefore have made a fourth change if he wanted to, but chose not to.