Barcelona appointed Ronald Koeman as their manager after parting ways with former head coach Quique Setien last year. The Dutchman took charge of the team during the 2020-21 campaign and had a fairly successful outing, winning the Copa del Rey trophy in his debut season.This term, though, things have turned upside down for the tactician. Barcelona are currently performing at a poor level. Many are calling for Koeman's sacking due to unfavorable results in recent games as well as accusations of drifting away from the club's core values in terms of playing style.Nevertheless, that takes nothing away from the positive influence the Dutchman has had at the club so far. The one thing that stands out is the development of certain members of the squad.Apart from integrating youngsters into the team, Koeman's spell has also seen a handful of players improve at the Camp Nou. Below, we highlight five such players.#5 Sergino DestThe defender is off to a promising start under Ronald KoemanSergino Dest joined Barcelona from Dutch outfit Ajax in a deal worth €21 million ahead of the 2020-21 campaign. The defender had a promising start to life in the Catalan capital, playing 44 games and recording three goals and one assist to his name across all competitions.Barça Universal@BarcaUniversalSergiño Dest: "I am in the right place to fulfill my potential. I have developed a lot at Barça, and I think the system we are using right now is something that suits me really well."4:04 PM · Mar 24, 202194031Sergiño Dest: "I am in the right place to fulfill my potential. I have developed a lot at Barça, and I think the system we are using right now is something that suits me really well." https://t.co/U8F4Y66c42After playing his first few games for Barcelona last season, it was evident the 20-year-old still had some work to do, especially in defending. Working with Ronald Koeman, he improved gradually as the campaign progressed and finished among the top performers in the team.This season, though, Dest has taken his game a step further. The USMNT star has played eight games for the Blaugrana, putting up spectacular displays on either side of the defense. So far, he's recorded 14 tackles, nine blocks and six clearances, as per Whoscored. He's also recorded one assist to his name.#4 Oscar MinguezaRonald Koeman has used Oscar Mingueza in seven games so far this seasonRonald Koeman promoted the Spaniard to the senior team last season and integrated him into the backline. Oscar Mingueza made 41 appearances in Barcelona's jersey during the campaign, contributing two goals and three assists in all competitions.Goal@goal🗣️ Barcelona debutant Oscar Mingueza: "I spent all week wondering if I would play or not and when I found out I was so happy."I hope that this is the start of something big." 🙏07:40 AM · Nov 25, 2020203649🗣️ Barcelona debutant Oscar Mingueza: "I spent all week wondering if I would play or not and when I found out I was so happy."I hope that this is the start of something big." 🙏 https://t.co/iVTbX0cGbGThe defender has displayed tremendous improvements in recent games, playing with more confidence, calmness and composure. He's alternated between the center and right wing of the backline this season, putting up a couple of decent displays in seven appearances.