Manchester United boss Jose Mourinho says certain players are not starting games because he carefully analyses opposition before every game.
The likes of Henrikh Mkhitaryan and youngster Marcus Rashford started last Friday's game against Southampton on the bench.
But the Portuguese says they will feature on a more regular basis from next month.
"Every player is working hard and performing well," Mourinho told MUTV.
"But every match is a match and I analyse the opponent and my team.
"I try to choose the best players and I know that nothing can change the frustration of the players that are not selected to play.
"But the reality is they all know they belong to a group of 23. To belong to that group, you must be a really good player, and they all are.
"At this moment, they feel the situation because it's one match a week but September is around the corner and, in September, everybody is playing."