It's fair to say that Manchester United are no longer the team they once were.A side known for their consistent domination of the Premier League seems a shadow of their former selves in today's context. Their squad boasted several world-class players at one time but the club is going through a transition phase currently.United are by far the most successful side in English football history. The Red Devils have won a record 13 Premier League titles, 20 overall English first division titles and three UEFA Champions League titles.Their last trophy, however, came in 2017 when they won the UEFA Europa League. Ever since the departure of Sir Alex Ferguson, the side has found itself in a state of constant flux.Several managers have tried to fill the shoes of the legend but have failed to meet the lofty expectations. United have also spent several million euros in the transfer market trying to strengthen their squad but have often failed to reap the benefits.Let's take a look at five world-class players Manchester United have failed to replace:#5. Nemanja VidicManchester United v Hull City - Premier LeagueNemanja Vidic is one of the best defenders in Manchester United's history.The Serbian joined the Red Devils in 2006 and went on to enjoy eight successful years with the Manchester outfit. During his time with the club, Vidic won five Premier League titles and one UEFA Champions League trophy.B/R Football@brfootballPremier League: 🏆🏆🏆🏆🏆 Champions League: 🏆 League Cup: 🏆🏆🏆 Club World Cup: 🏆 Community Shield: 🏆🏆🏆🏆🏆 Manchester United signed Nemanja Vidic on Christmas day in 2005. It worked out 🎄9:16 AM · Dec 25, 2020193691685Premier League: 🏆🏆🏆🏆🏆 Champions League: 🏆 League Cup: 🏆🏆🏆 Club World Cup: 🏆 Community Shield: 🏆🏆🏆🏆🏆 Manchester United signed Nemanja Vidic on Christmas day in 2005. It worked out 🎄 https://t.co/TFV4rjhXgwVidic is regarded by many as the perfect Premier League defender. A hard-tackling player, he was known for his incredible judgment and aerial prowess. Vidic forged a formidable pairing with Rio Ferdinand at the heart of the Manchester United defense.Vidic left the club in 2014 to join Inter Milan, but the club have yet to find a suitable replacement for the legend. The likes of Harry Maguire and Victor Lindelof have tried to fill Vidic's shoes but have only come up short in comparison so far.#4. Rio FerdinandManchester United v Fulham - Premier LeagueRio Ferdinand is one of the most decorated defenders in Premier League history.The Englishman was signed from Leeds United in 2002, becoming the most expensive footballer in history at the time. Ferdinand was well known for his excellent distribution and precision in the air.B/R Football@brfootballPremier League: 🏆🏆🏆🏆🏆🏆League Cup: 🏆🏆Community Shield: 🏆🏆🏆🏆Champions League: 🏆Club World Cup: 🏆17 years ago, Manchester United broke the British transfer record to sign @rioferdy5 from Leeds.3:44 AM · Jul 22, 20196633905Premier League: 🏆🏆🏆🏆🏆🏆League Cup: 🏆🏆Community Shield: 🏆🏆🏆🏆Champions League: 🏆Club World Cup: 🏆17 years ago, Manchester United broke the British transfer record to sign @rioferdy5 from Leeds. https://t.co/OZTwnQAM33Ferdinand spent 12 years with the Red Devils, winning a host of trophies and individual awards. He won six Premier League titles, three English League Cup trophies and one UEFA Champions League first-place medal in his time at Old Trafford.He also featured very regularly in the Premier League team of the year, a feat that has yet to be matched by his successors. Ferdinand and Vidic together formed one of the most successful centre-back pairings in Premier League history.