The England forward had an outstanding campaign last term, scoring 30 goals in all competitions.
However, Rashford has struggled this term and was dropped for a 2-1 win over Chelsea on Wednesday night.
Ahead of a weekend game against Bournemouth, Ten Hag said to reporters: "So Rashford is an incredible, good player.
“You can't do it with 11 players, he can't play every game, he's not in this moment in the form he was last year but I am sure he will get there.
"As manager, my coaches, with the rest of the staff, we always consider but the next game is always the most important, especially in the Premier League where everyone is killing everyone, you need a strong team."
"I think we have a squad and in the squad there is internal comp, if you want a successful season you need more than 11 players. Finally, in every season, it will turn and in every season it's what is the best team. That's what you expect from every player, there has to be dedication to aim for this."