Maguire was re-appointed captain by new boss Ten Hag in the summer but after starting the first two games of the season was dropped for the 2-1 win over Liverpool on Monday.
Ten Hag says Maguire will continue to act as club captain but, speaking at a news conference on Friday, offered the England defender no assurances about his prospects as a regular starter.
"I think it doesn't mean when you are captain you are established to play always, especially when you also have [Raphael] Varane in your squad."
Varane won plaudits for his performance alongside Lisandro Martinez in defence against Liverpool but Ten Hag said he was also impressed with Bruno Fernandes, who wore the captain's armband in the absence of Maguire.
"We have a leader group and Harry is one of them," added Ten Hag.
"Bruno is one of them. Bruno did quite well as captain. He led by example and he brings so much energy to the team in and out of possession."
Maguire has been a regular at United since his £80m move from Leicester in 2019.
But with Varane arriving from Real Madrid last summer and Martinez signed by Ten Hag ahead of his first season in charge, the Dutchman hinted that Maguire will have to get used to being rotated in and out of the team.
"We have options," said the United boss.
"Varane, his stature is immense and in preseason we took a decision to build him physically so he had a bit of a slow start.
"His profile, his stature and what he won already in the past shows he can really contribute to his team. For the team there is competition, and we need that. We have to cover so many games.
"Victor Lindelof did really well in preseason so I am happy that he will be back in the squad so we will have another option. We have competition internally and that's good and that is what top teams need."