In the Clasico, he had Antoine Griezmann ready to come on, against Juventus it was Ansu Fati and before that it was Philippe Coutinho when facing Getafe.
The Dutchman has made it clear that he wants to capitalise on the depth of his squad and is showing that in each and every game, having used 29 of a possible 35 changes from seven games.
In every game, other than against Celta Vigo, he has used at least four of the five substitutes available to him.
That is a symbol of the trust that he has in his players available on the bench alongside him, with 20 different players so far having been used in seven games in LaLiga Santander.
If you include European competitions, that figure goes up to 22 different players used.
Only Junior Firpo and Carles Alena have not been used in the league this season, alongside Samuel Umtiti who has been injured.
Riqui Puig’s role has not been as significant as many fans had hoped and expected, but he has played, albeit in only a brief appearance as a substitute against Getafe.
Other players have seen themselves too far from the starting line-up but able to make an impact, like Francisco Trincao.
The Portuguese youngster is one of a select club of players to have played in every LaLiga Santander game this season, having appeared in every fixture from the bench.
Martin Braithwaite plays a similar role, having come on in all of the last four games that Barcelona have played.
Such depth and belief in his squad gives Koeman a chance to rest key men, like Messi against Betis, and no-one is safe from changes.