Four years since his return to Manchester United, Paul Pogba has been a pale shadow of the player who enthralled the Juventus faithful with his silken skills and world-class performances.However, the Frenchman struggled to retain a regular first-team place under Jose Mourinho and the same script seems to be unfolding under current Manchester United manager Ole Gunnar Solskjaer as well.Despite his undoubted talent, the 2018 FIFA World Cup winner has simply failed to produce the goods at Manchester United.In fact, in recent times, the embattled midfielder, who was rumored to leave Manchester United in the last few transfer windows, has proven to be a huge liability for the club. Pogba has conceded three penalties - the most by a Manchester United player under Solskjaer - despite mostly operating in the center of the park.3 - Paul Pogba has conceded three penalties in the Premier League under Ole Gunnar Solskjaer, while no other Manchester United player has conceded more than one. Discipline. pic.twitter.com/ZXL2OrWAxp— OptaJoe (@OptaJoe) November 1, 2020Manchester United could cut their losses and sell Paul Pogba in 2021Pogba seems to have the support of Solskjaer for now, despite his high-profile frailties and general insipidity on the field.However, the Frenchman's tally of just three goals and six assists in his last 35 games in all competitions for the club is a very underwhelming return from a player touted as a world-class midfielder by many.At 27, Pogba is only approaching his prime but at the moment, he seems to have hit the ceiling at Manchester United and probably needs a move away from the club to revive his flagging club career.On that note, let us have a look at five players who could replace Paul Pogba at Manchester United.#5 Ryan GravenberchRyan GravenberchLikened with Manchester United's Paul Pogba, Ryan Gravenberch is one of the most exciting prospects to have emerged from Ajax's famous De Toekomst academy.Last season, the versatile central midfielder, who can also play as a defensive midfielder, became the youngest Eredivisie debutant for Ajax.16 - At the age of 16 years and 130 days, Ryan Gravenberch is the youngest player to make his debut for @AFCAjax in the Eredivisie. Extended. pic.twitter.com/FGf7qjuqzJ— OptaJohan (@OptaJohan) June 11, 2020Gravenberch's composure in the middle of the football pitch belies his age. His positional awareness and versatility are impressive for a player of his age and these are attributes that could see him flourish at Manchester United.Former Netherlands international Ronald de Boer thinks that Gravenberch is a more promising prospect than a certain Matthijs de Ligt, who led Ajax to a fairytale run to the Champions League semi-finals in 201-19. He said:"Matthijs might have been exceptional at that age, but Gravenberch has unrivalled qualities."#4 Eduardo CamavingaEduardo CamavingaEduardo Camavinga, who is touted as a generational talent, plies his trade for Ligue 1 club Rennes. The Angola-born French midfielder showed maturity beyond his age and played a key role in ensuring Rennes' qualification for the Champions League last season.Camavinga's tactical intelligence and versatility are his biggest attributes. Although goal-scoring remains a work in progress for him, the teenager became France's second-youngest goal-scorer ever when he scored for Les Bleus against Switzerland.Camavinga, who is already on the radar of top European clubs like Manchester United and Real Madrid, has impressed his Rennes coach Julien Stephan, who wants the prodigy to remain at the French club for at least another season."It would do him good to stay at least one more year at Rennes because he needs to back up what he's done. He's in a place he knows well. He is at a club that has enormous trust in him, and he is surrounded by people who knows him perfectly," said Stephen about his star player.However, the teenager may not see out the remainder of his contract at Rennes. That is because Manchester United could reportedly snap up Camavinga for £45 million, as there are serious doubts over Paul Pogba's long-term future at Old Trafford.