Arsenal won the FA Cup last season and started the new season by lifting the FA Community Shield.If only these two pieces of silverware were enough to talk about Arsenal's form since last season. An eighth-place finish in the 2019-20 Premier League does not paint the complete picture as Arsenal's two recent trophies would suggest.It was an erratic season at the Emirates Stadium, to say the least. There were two managerial changes, a lot of instability in the boardroom and inconsistent performances on the pitch that led to unrest and backlash from the fans.The low point of Arsenal's 2019-20 season was the sacking of Unai Emery in November. The Spaniard was supposed to be the man to carry Arsenal to domestic and European success, given his track record with Sevilla in the Europa League.However, after a run of indifferent results, the Arsenal board decided to give Emery the sack. Former player Mikel Arteta, who was Pep Guardiola's number two at Manchester City and earmarked for success by his mentor, was brought in to transform the club's fortunes.Welcome back, Mikel! 👋Head coach of The Arsenal 👔 pic.twitter.com/lhsAfQ7cfq— Arsenal (@Arsenal) December 20, 2019Since the hiring of Arteta, Arsenal have had a slight resurgence in form and are playing a style of football that the fans have come to appreciate.After winning the FA Cup to qualify for the Europa League, Arsenal wasted no time in making additions to their squad this summer. They acquired Willian on a three-year deal from Chelsea and bought Gabriel for €30 million from Lille while William Saliba arrived after his loan spell with St. Etienne.However, there is one area of the field where Arsenal lack depth and quality: it is at the back. That has been the case with the North London club since the days of Arsene Wenger as defensive frailties have blighted Arsenal over the years. Therefore, bringing in personnel to bolster their defence could significantly improve Arsenal's performances in various domestic competitions and in Europe.5 players who could help solve Arsenal's defensive problems:#5: Dayot Upamecano (RB Leipzig)Dayot Upamecano showing his aerial prowess against Atletico Madrid.21-year-old French centre-back Dayot Upamecano has been a revelation during the last two seasons while playing for German club RB Leipzig.His strong performances in the knockout rounds of the 2019-20 Champions league helped Leipzig reach the semifinals of the competition for the first time. Upemecano was also a key player in the Bundesliga last season as Leipzig finished a creditable third.Dayot Upamecano has been linked with a host of top European clubs, with Manchester United reportedly set to trigger his release clause this summer. Barcelona have also registered interest in Upamecano. That gives Arsenal a lot of competition to deal with if they decide to enter the race for the Frenchman.The RB Leipzig defender would add pace, physicality and stability to Arsenal's defence which has lacked any sort of consistency and reliability in recent times. Upamecano will, however, not come cheap and may not be on the wishlist of Mikel Arteta, given the limited spending capacity of Arsenal this summer.#4: Samuel Umtiti (FC Barcelona)Samuel Umtiti has been made available by FC Barcelona.Samuel Umtiti seemed to have the world at his feet after forming a successful centre-back pairing alongside Raphael Varane in France's victorious 2018 FIFA World Cup campaign. Prior to that quadrennial tournament, Umtiti enjoyed two successful seasons at Barcelona where he made the centre-back position his own alongside Gerard Pique.However, post the World Cup, Umtiti has been afflicted by numerous injuries that have led to a dip in his form and Barcelona signing fellow Frenchman Clement Lenglet from Sevilla for €35 million.After being reportedly told by new Barcelona boss Ronald Koeman that he does not have a future at the club, Umtiti has been put up for sale to raise funds for new player arrivals.At 26, the Frenchman is still young and possesses all the qualities and physical attributes required to succeed in the Premier League. He would be a valuable acquisition for any top Premier League club, especially Arsenal whose defenders lack the speed and physicality of Umtiti.