Arsenal’s lineup for their first game of the season against Newcastle contained a few surprises. Unai Emery was clearly keen to ease his new signings into action, with Dani Ceballos, David Luiz, Nicolas Pépé and Gabriel Martinelli all taking their seats on the bench at St James’ Park. The manager selected a team that included four players aged 21 or under. Ainsley Maitland-Niles (21) and Mattéo Guendouzi (20) were given plenty of minutes last season but the travelling fans would not have expected to see 19-year-olds Joe Willock and Reiss Nelson on the field. We may not see that line-up again any time soon, but Emery’s selection was perhaps a sign that Arsenal do not want more promising youngsters to leave the club before they have been given opportunities to prove themselves in the first-team. Krystian Bielik left Arsenal for Derby County this summer without so much as a League Cup start for the club. The transfer frustrated some supporters, who have seen a number of the club’s youth products make big impressions elsewhere over the past year. Bielik certainly did so while on loan at Charlton last season – his performances at centre-back helped the club earn promotion to the Championship – and some Arsenal fans were hoping the 21-year-old would be given a chance to impress in their defence. The £10m fee was considerable, but he may yet become one that got away. Bielik is yet to play for Derby in the Championship yet this season but another former Arsenal youngster, Jeff Reine-Adelaide, made the quite the impression in his first game of the season in Ligue 1. Reine-Adelaide ran the show for Angers as they came from behind to win 3-1 against Bordeaux (who, incidentally, had left former Arsenal captain Laurent Koscielny on the bench). The midfielder initially signed for the club on loan in January 2018 but Arsenal sanctioned a permanent deal last summer for a little over £1m. He would be worth a lot more now. The 21-year-old levelled the scoring on Saturday night, set up Angers’ third goal and completed a remarkable nine dribbles. He was the standout player of the weekend in the league. Reine-Adelaide has thrived since moving to a more central position in France. He scored three goals for Angers in the last few weeks of last season and continued his good form in the summer, scoring a brace for the France Under-21s against Belgium in a friendly before setting up goals in matches against England and Croatia in the European Championship. Lyon were clearly impressed. They have agreed a €30m transfer with Angers for the player this week. Arsenal may come to rue the day they let Reine-Adelaide leave and they should also be wondering whether selling Ismael Bennacer was poor judgement. The Algerian left Arsenal for Empoli in 2017 and became a first-team regular immediately. Within two months in Serie B, he earned his first senior international cap and he played a pivotal role in his new club’s promotion to the top flight that season. He was unable to prevent Empoli from heading straight back down to the second tier but he made his mark among Italy’s elite. The dynamic midfielder won possession more times in the middle third than any other player, completed the most dribbles of any central midfielder and boasted the best success rate from said take ons in the league. He carried that form into the Africa Cup of Nations this summer, starting every game to help inspire Algeria to their first title in 30 years, setting up three goals and being named player of the tournament in the process. Many Arsenal fans were keen to see the club sign the youngster back from Empoli, but Bennacer instead stayed in Italy, signing for Milan for £14.5m. Arsenal had sold him for less than £1m. Then, of course, there is the most regrettable of the lot. Serge Gnabry has gone from strength to strength since leaving the Emirates. Sold to Werder Bremen for £4.5m in 2016 following a dismal loan spell at West Brom, the German would now cost 10 times that figure. He scored scored 11 goals in his first Bundesliga season, earning a move to Bayern Munich, who loaned him out to Hoffenheim. The forward scored another 10 goals in 20 league starts for Hoffenheim, earning a recall to Bavaria last summer. He scored 10 league goals for Bayern last season – the third season running he has hit double figures in the Bundesliga. Gnabry is now a regular in the Germany team, for whom he boasts an outstanding record of seven goals in eight caps. He was named Bayern’s player of the year last season despite starting just 21 of his 30 appearances. Now 24, he looks set to be a key player for one of Europe’s elite clubs for years to come. All clubs end up seeing players who they have deemed surplus to requirements come good at one stage or another, but Arsenal can learn from the experience and look forward rather than back. That means offering young players a chance to prove their worth in the Premier League, a principle set in motion at St. James’ Park on Sunday. The Guardian Sport