#3 Jack Wilshere
Jack Wilshere joined the club at the young age of 9 and he never looked back to some extent. He became the youngest ever player to play for Arsenal in the Premier League at the young age of 16 years and 256 days. Just like Walcott, he looked set to become a future star, but injuries meant that he never managed to reach his full potential.
He left the club at the end of the 2017/18 season after Unai Emery said that he would not be in his plans for the upcoming season. He now plays for West Ham and gets a lot of playing time, but he sadly will never be the player that he once was.
#2 Serge Gnabry
Serge Gnabry rose to fame during the 2013/14 season with Arsenal after some impressive performances. Some even said it would be likely that he would make the Germany World Cup squad. However, he picked up an injury against Bayern Munich, which damaged the remainder of his time at Arsenal.
He left to play in Germany, and he now plays for Bayern Munich. He is playing very well and the 23 year old is definitely a future star in the making.