The England international has fallen down the pecking order behind Lisandro Martinez, Raphael Varane and Victor Lindelof, with even left-back Luke Shaw having played in central defence, leaving Maguire with eight starts in the league this season.
Maguire became the world's most expensive defender when United signed him from Leicester City for £80 million in 2019. His contract is due to end in 2025.
Asked about Maguire's future, Ten Hag told The Times newspaper: "Let's say I'm happy he's here and when we needed him he did his job. But it's also a decision he has to make."
The Dutchman said Maguire was putting in 100 per cent effort in training and had played an important role as club captain but acknowledged the player would not settle for a place on the bench going forward.
"No one would be happy with this situation. He is not as well," he added.
Ten Hag added that goalkeeper David de Gea will remain at the club next season but said the Spaniard, who kept the most clean sheets in the Premier League this season, would face competition for the gloves.
"I will not say he'll always be my number one because in a club like Man United there must be competition in all positions," he said.
'Legacy'
United finished third in the league and won the League Cup in Ten Hag's first season as manager. They have the chance to add another trophy when they face champions Manchester City in the FA Cup final on Saturday.
"I've seen many FA Cup finals. The tradition. I'm really looking forward to it," Ten Hag said. "It's not about stopping Manchester City, it's about us winning the FA Cup. We want to build our own legacy and era."
United have had little to celebrate since winning their last league title in 2012/13 under Alex Ferguson, but there is a growing feeling of optimism thanks to Ten Hag's tactical acumen and man-management skills.
The Dutchman keeps in touch with Ferguson.
"With all his experiences and his intelligence it's really valuable to talk with him. From Sir Alex, I learn a lot because he's such a legend. It gives me inspiration, how to manage," Ten Hag added.
"After Sir Alex left, the culture changed over the years. One of the biggest qualities Sir Alex had was to have high standards.
"I wanted to bring it back in, so that everyone in this organisation lives the highest standards and the football players too."
