Manchester United is set for a busy summer transfer window after appointing new manager Erik Ten Hag following an unsuccessful 2021-22 season in the Premier League. United's sixth-placed finish will certainly not sit well with fans or the board, who will be looking for vast improvements next year. Many players are expected to see their time at the club come to an end, and rightfully so. Slews of Manchester United players have failed to live up to expectations over the past few years, and the club needs to make some big changes to the roster.

That said, there are a handful of key players that have been linked with possible moves away from Manchester that simply must be retained if the team is to turn its woeful performances around. Simply going out and spending $500 million in the transfer market won't guarantee success, as United certainly needs to build better team chemistry if they're to stage a title run.

With all that in mind, keeping certain players at the club will be a critical goal for Manchester United this summer, and these four players should be retained by any means necessary.

4 players Manchester United can't sell in summer transfer window

4. Dean Henderson

While Dean Henderson has aspirations of being a starting goalkeeper, allowing him to leave Manchester United would be a big mistake for the club. David De Gea is extremely talented, but the Spaniard is prone to inconsistent spells, and struggles in the air. Having Henderson around to compete for the starting spot will get the best out of both goalkeepers, as De Gea will know his job is anything but secure, while Henderson will be doing his all to dethrone the 31-year-old and climb out of his shadow at the club. While there's sure to be interest from other clubs in Henderson's services this summer, United could send a message to both goalkeepers by expressing their desire to keep him at the club.

3. Donny van de Beek

Donny van de Beek never got a fair shot at Manchester United. Seemingly outcasted by Ole Gunnar Solskjaer, van de Beek was shipped off on loan to Everton when Ralf Rangnick took over. Now that his former manager in Erik Ten Hag is joining the club, this is the perfect opportunity for van de Beek to prove he has the quality to earn a place at Manchester United. Who better to bring out the potential he once showcased than the manager who helped him develop into a must-see talent at Ajax? The midfielder has a chance to prove all of his doubters wrong this season, and he'll be chomping at the bit to get some real playing opportunities in Manchester.

2. Fred

Fred's early-season struggles feel like a thing of the past, and he's since become a pretty important part of Manchester United's midfield setup. While the club should certainly explore bringing in more talent to the midfield in the summer, keeping Fred on the squad would be the right move. He has the ability to change the game and pull the strings in the midfield when he's at his best, and his late-season improvements showed he should be given a longer leash at the club. While the club likely shouldn't depend on Fred as an everyday starter, he'll be an important piece for Manchester United should they opt to keep him at Old Trafford.

1. Diogo Dalot

The young fullback is out of contract in 2023, but Manchester United must do everything they can to prevent him from leaving. With Aaron Wan-Bissaka looking likely to leave the club this summer, Dalot will have the opportunity to claim the role of starting right-back all for his own. He overtook Wan-Bissaka on the depth chart last season and while he's not the most sound defensive fullback, he's very capable in the attacking third. At just 23 years old, Dalot could develop into a key part of Manchester United's defense.