#3 Lucas Digne (Aston Villa)

Lucas Digne is another Barcelona outcast who is doing considerably well in the Premier League. He recently joined Aston Villa from Everton and has shown great performances in the few matches he has played for Villa.
He represented and won the FIFA U20 World Cup in 2013 with France. Digne's performance earned him a spot in the senior squad during France's 2018 FIFA World Cup and 2020 EURO Cup outings.
He signed a five-year deal with Barcelona in 2016. The French international enjoyed recurring playing roles and was a regular figure on the pitch during Ernesto Valverde's reign. He eventually joined Everton for more playing time.
Digne's skillset would have been handy for Barcelona, who are in trouble regarding their back four.
#2 Emerson Royal (Tottenham Hotspur)

Emerson Royal's saga with Barcelona was not the usual one. The full-back was an Atlético Mineiro player when the Catalan club and Real Betis decided to sign him as part of a joint financial operation between the clubs.
Royal joined Betis during the 2018-19 season with a clause that allowed Blaugrana to sign the Brazilian later. They exercised this option during the closing stages of the 2021 summer transfer window only to let go of him on deadline day.
Royal is now a regular at Spurs and one of the favorites under manager Antonio Conte. Should Barcelona have decided to keep him, Xavi would have found his answer to the wingback problems.
#1 Philippe Coutinho (Aston Villa)

Philippe Coutinho's story is somewhat similar to Emerson Royal's. The forward was a hot property for Liverpool and was under Barcelona's radar throughout the 2017-18 season.
Coutinho left Liverpool mid-season in 2018, much to the disappointment of the club and its fans. He joined Barcelona for a reported £142 million fee with the hopes of laying his hands on the coveted Champions League trophy.
Coutinho was signed as a potential replacement for Andres Iniesta. However, things didn't work out between the two parties, and the Brazilian was sent on loan to Bayern Munich in 2019. At Bayern, Coutinho played a part in the Bavarian's 8-2 maraud against Barcelona in the Champions League quarter-final in 2020.
He returned to Barcelona the following season, but the club could not provide him with a permanent place. Coutinho returned to the Premier Leauge in January 2022 with Aston Villa. He was reunited with the former club teammate and now his coach, Steven Gerrard.
A small amount of patience with Coutinho would have helped the struggling Barcelona at the moment.