In Man United news, 30-year-old England defender, Harry Maguire made only 16 appearances in the Premier League for United this season.
Lisandro Martinez and Raphael Varane have been Ten Hag's preferred centre-back pairing in his first season in charge at Old Trafford.
"No-one would be happy with this situation," Ten Hag told The Times.
Manchester United boss Erik ten Hag says Harry Maguire 'has a decision to make' over his future at the club 🔴 pic.twitter.com/ab5GAkQmZG
— Sky Sports News (@SkySportsNews) May 29, 2023
"He is not as well. He trains always on best levels, so with 100% effort.
"So he handles that situation well and he's in that manner and in his captaincy he's important for the squad."
Maguire has made some costly errors this season, most recently in last month's 3-0 Europa League defeat by Sevilla.
Ten Hag added: "He has high competition there
🚨BREAKING: Paul Heckingbottom is interested in signing Harry Maguire from #mufc, sheffield United is looking for an experienced CB, and Harry Maguire fits the role. pic.twitter.com/N4PCF83B6F
— Sky Sports Premier League (@SktSportsPL) May 28, 2023
"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."
Maguire arrived at United in 2019 from Leicester for £80m, a world-record fee for a defender, and his contract runs until 2025.
He played in all five of England's World Cup games in 2022 and has been selected for the upcoming Euro qualifiers, but manager Gareth Southgate has said he is concerned by his lack of playing time at United.
While Ten Hag did not confirm whether Maguire would be a United player next season, the former Ajax boss said that goalkeeper David de Gea would be staying for the 2023-24 campaign.
In other Man United news, De Gea has been the club's first-choice keeper this season and won the Golden Glove award for the most clean sheets in the Premier League.
Erik ten Hag issues Harry Maguire with a STAY-OR-GO ultimatum as he insists the out-of-favour Englishman has a 'decision' to make on his future at Old Trafford https://t.co/Bh5fVWmQT3
— MailOnline Sport (@MailSport) May 29, 2023
Asked if the 32-year-old would still be at Old Trafford next season, Ten Hag replied: "Yes, but I will not say he will always be my number one because in a club like United there must be competition in all positions."
United play Manchester City in the FA Cup final at Wembley on Sunday with the hope of denying their city rivals' bid to match the Treble won by Sir Alex Ferguson's team in 1999.