Former Southampton striker Kevin Phillips recently spoke about how Manchester United's transfer plans could help Harry Maguire.According to Bild, United are looking to sign Chelsea defender Antonio Rudiger, who could leave the Blues on a free transfer. The German has just six months left on his contract and negotiations with the club have so far failed.Meanwhile, Manchester United's defense has faced a lot of criticism this season. Much of it has been directed towards club captain Harry Maguire, who has been poor this season in a number of matches.His individual errors have led to United conceding numerous goals, most notably against Leicester City and Liverpool.Christian Falk@cfbayernTRUE✅ @ManUtd is interested in @ToniRuediger - Ralf Rangnick knows his Agent and Brother Sahr Senesie very well and signaled willingness to negotiate2:49 AM · Dec 15, 20213617402TRUE✅ @ManUtd is interested in @ToniRuediger - Ralf Rangnick knows his Agent and Brother Sahr Senesie very well and signaled willingness to negotiate https://t.co/6Xz4nZ2u4TPundit Kevin Phillips believes the rumors linking Rudiger with Manchester United could spur Harry Maguire on to work harder for his place in the team. Speaking to Football Insider, Phillips said:"Rudiger would be serious competition. I think Maguire would handle it with no problem whatsoever. A player of Rudiger's calibre might actually help Maguire. It might up his game and get the best out of him."It would be a big statement if United did bring in another centre-half like Rudiger. The pressure would certainly be on Maguire if it happened."He also highlighted the importance of competition at big clubs like Manchester United by adding:"You want competition for places at a club like Manchester United though. That is how you get the best out of players week in, week out. It has not been a great season for Maguire but he is a quality player."Manchester United's defensive troubles this season do not end at Harry MaguireManchester United signed star defender Raphael Varane from Real Madrid this season. He was seen as a defensive partner with Harry Maguire and a replacement for Victor Lindelof.However, the Frenchman has been able to make just nine appearances this season in all competitions. He has had to spend much of his time out due to injuries.Reddevilscorner8@Reddevilscorne8Next time when we are playing, Rapha will be available for selection #raphaelvarane #MUFC5:19 AM · Dec 20, 20211Next time when we are playing, Rapha will be available for selection #raphaelvarane #MUFC https://t.co/8fZ2we4qRoMeanwhile, Manchester United's only other proper centre-back option is Eric Bailly. The Ivorian has impressed whenever he has played but still hasn't made it to the manager's starting lineup.Harry Maguire has made multiple mistakes but under interim manager Ralf Rangnick, he has looked like a better player.Fighting in many different competitions, Manchester United would want to have more options to lead their defense.Hence, signing Antonio Rudiger would not only be a boost for Maguire to perform well but also give United the squad depth a top club needs.