Manchester United have enjoyed a good pre-season under new boss Erik ten Hag. They have signed new players in Lisandro Martinez, Tyrell Malacia and Christian Eriksen.The Dutch boss is attempting to implement his style of play at Old Trafford. Their first test will come this weekend in the form of Brighton and Hove Albion in the Premier League.Ten Hag's expansive footballing philosophy means Manchester United still need a few more players at the club who can accurately execute the manager's vision. There has also been a mass exodus of players at the club this summer with Edinson Cavani, Paul Pogba, Juan Mata, Jesse Lingard, and Nemanja Matic all gone from Manchester United.This means Manchester United need to add new faces to the squad ahead of the new season. Here are three positions that the club needs to address first:#1 Defensive midfielderFred and Scott McTominay have been Manchester United's regular starting midfielders in deep positions along with Nemanja Matic, in rotation. With Matic gone, the club are now short of depth. Moreover, neither Fred nor McTominay had a good season last time out. Young Alejandro Garnacho needs more time to establish himself at the club.Fred and Scott McTominay tussling for the ball.The club, in fact, have been in need of quality defensive midfielders for several seasons now. They have been linked with a move for Barcelona's Frenkie de Jong throughout the summer, but a move is yet to materialize.Manchester United need a ball-playing number six who can organize the defense while playing the ball out of the back.#2 Right-backManchester United thought they have a quality player in Aaron Wan-Bissake when the club signed him from Crystal Palace for £50 million in 2019. However, the English international, despite being good defensively, has fallen short in attack. It is a necessary qualiy in most modern-day full-backs to be able to romp forward with the ball. The likes of Chelsea, Manchester City and Liverpool have been blessed to have players like Reece James, Joao Cancelo and Trent Alexander-Arnold in their ranksDiogo Dalot is expected to be first-choice for United this season.United's other option Diogo Dalot is better at moving forward but lacks the correct defensive acumen. It means that neither of the two first-team right-backs are good enough to start for Ten Hag.They need a new signing in that position, preferably a young player who can occupy the position for years. #3 Right wingerThe Red Devils signed Jadon Sancho last summer, who had shined at right-wing for Borussia Dortmund (114 goals and assists in 136 games). However, the English youngster has failed to replicate that form at Old Trafford. He was shifted to the left-wing by former interim boss Ralf Rangnick, which seemed to have helped the player. Moreover, Mason Greenwood had made that right-wing position his own until recently However, with Greenwood now indefinitely suspended, United have a glaring hole in that position. United have been heavily linked with Antony.The club needs new attackers to occupy that slot. Antony from Ajax has been linked with a move for quite some time now, but once again the move is yet to materialize. Ten Hag's former association with the Dutch club could pave the way for a move in the next few weeks.