Manchester United are currently struggling to leave the midtable doldrums and return to the top-four position that fans and pundits had predicted. It's a far-cry from the start of the season when the Red Devils seemed to pack a star-studded title-contending squad. At this rate, if they make it into the top-four by the turn of the new year, it would be an admirable feat.It wasn't always like this for Manchester United. Long before the scurry of managers came to Old Trafford, Sir Alex Ferguson guided United across the echelons of world football.During the 90s, Ferguson managed the Red Devils to an astonishing 19 trophies. While this number reduced across 2000s, the club maintained their massive world-class status.Manchester United@ManUtdSir Alex Ferguson was appointed United boss 3️⃣5️⃣ years ago today. The rest is history ❤️#MUFC | #OnThisDay9:03 AM · Nov 6, 2021480064723Sir Alex Ferguson was appointed United boss 3️⃣5️⃣ years ago today. The rest is history ❤️#MUFC | #OnThisDay https://t.co/nypDtsO518Managers like David Moyes, Louis van Gaal and Jose Mourinho have also played their part in the club's history. However, many of United's most influential signings came during Ferguson's era. But the club has also made some impactful signings after the era of Sir Alex Ferguson. So without further ado, let's take a look at:Five such signings for Manchester United during the 21st century#5 Bruno FernandesManchester United v Atalanta: Group F - UEFA Champions LeagueAfter spells with Udinese, Sampdoria, and Sporting, the star Portuguese playmaker joined Manchester United for an initial fee of €55 million in January 2020. Although the star has played just one full season for the Red Devils, his impact on the squad has been massive.In his debut season, Fernandes scored 12 goals in 22 appearances to rejuvenate United's attack. He also won the 'Sir Matt Busby Player of the Year' award even though he played only half the season.Last season, in his first full season at Old Trafford, Fernandes scored 18 goals. He also assisted 12 in 37 Premier League games, remarkable figures for a midfielder.This season has already seen the star score four goals and assist seven across 16 appearances in all competitions. It's quite clear that Manchester United would be in a worse state without Fernandes' overall input on the field.#4 Rio FerdinandWolverhampton Wanderers v Manchester United - FA Cup Third RoundRio Ferdinand joined Manchester United from rival Leeds in 2002 for a whopping £41.5 million. The legendary defender guided the Red Devils' defense to new heights during a trophy-laden decade. Ferguson's eye for young talent noticed the star's capacity in the first third. Soon enough, Ferdinand became one of the best central defenders in the world.Manchester United@ManUtdWishing our former captain a happy birthday 🙌#MUFC | @RioFerdy51:33 AM · Nov 7, 2021297161721Wishing our former captain a happy birthday 🙌#MUFC | @RioFerdy5 https://t.co/uQFN1Y4wJbWhile his individual brilliance was notable, his pairing with Serbian legend Nemanja Vidic formed one of the strongest defensive partnerships in the Premier League. Ferdinand remained with United until after Ferguson left the club in 2013. His leadership for the Red Devils was showcased on the pitch until the very end when the star was 35.