Manchester United enjoyed an excellent 2020-21 season in the Premier League. Finishing in second place, the club can boast several positives from the season, including their away record and their goalscoring prowess.Although they did lose the UEFA Europa League final, they made up for it by finishing second and booking their place in the UEFA Champions League for next season. It goes without saying that while the squad looks good, there are several positions that require improvement if United are to challenge the biggest teams in Europe.On that note, let's take a look at five players Manchester United could sign this summer.#5 Kieran Trippier - Atletico MadridKieran Trippier in action for England in an international friendlyKieran Trippier has recently been linked with a shock move to Old Trafford. Although United already have one of the best defenders in the league in Aaron Wan-Bissaka, there have been numerous reports suggesting that his attacking ability is not up to the mark.Reports suggest that Ole Gunnar Solskjaer has plans to play Wan-Bissaka as a centre-back if Tripper is signed from Atletico Madrid. Trippier is coming off the back of an excellent season with Atletico, having won La Liga this year.Atlético Madrid turned down an opening proposal from Manchester United for Kieran Trippier. Price tag still around €40m to sell the right back. 🏴󠁧󠁢󠁥󠁮󠁧󠁿 #MUFC #Atleti...and Tom Heaton completed his medical with Manchester United today - he’s set to sign until June 2023. 🔴 #ManUtd— Fabrizio Romano (@FabrizioRomano) June 16, 2021With an asking price of £34 million, the 30-year old has already proven himself in the Premier League in the past with his former club Tottenham Hotspur. With Trippier's recent call-up to the national side and the interest of rival clubs, it remains to be seen if Manchester United can complete this transfer.#4 Raphael Varane - Real MadridRaphael Varane plays for Real Madrid in La LigaRaphael Varane is another name that has been constantly linked with Manchester United in the past.Currently with Real Madrid, the Frenchman has played for Los Blancos for ten years now. With a massively impressive CV, Varane has been unaffordable in the past for Manchester United. However, Solskjaer seems to have identified the need for another bonafide defender to partner Harry Maguire at the back, and Varane is a highly viable option.United make starting bid of £50m for Raphael Varane but Real Madrid demanding more #mufc https://t.co/ooum5nE8QE— Samuel Luckhurst (@samuelluckhurst) June 17, 2021The Frenchman had yet another good season with Madrid, finishing second in La Liga. He is also currently with the French squad at Euro 2020, where he commands a starting spot in defense.Manchester United's possible defensive lineups with Raphael Varane and Kieran Trippier #mufc https://t.co/gxUU5WxMN3— Man United News (@ManUtdMEN) June 23, 2021Valued at £63 million, Varane could prove to be outside United's budget considering their priorities to strengthen other departments. With the recent announcement of Sergio Ramos' departure, it seems further unlikely that Madrid will allow Varane to leave. Nevertheless, Manchester United remain interested, hoping to work out a mutually beneficial deal.