#3 Ismael Bennacer
Promising Algerian midfielder Ismael Bennacer arrived at Arsenal in the summer of 2015 after making his professional debut at French club Arles.
However, the then-teenager only played one game in two seasons at the Emirates before he was sold off to Serie B club Empoli.
Bennacer was only too happy to take the step down to the second division in a different country. The player bemoaned about Arsene Wenger playing him in an unfamiliar position led eventually led to him leaving the club.
"I was thrown on after two other injuries against Sheffield [Wednesday), played wide left in a trident attack, which I had never done before. I felt incredible pressure and wasn’t sure what was going on. I never played again after that. I had to be at a club where they really wanted me. I didn’t know Empoli, but I accepted a move down from the Premier League to Serie B because they were the club who wanted me the most," said Bennacer.
Since his departure from Arsenal, Bennacer has helped Empoli gain promotion to Serie A and now plies his trade for AC Milan.
The 2019 African Cup of Winner with Algeria has become a key player for the Rossoneri. Bennecer has made his name as a tenacious deep-lying holding midfielder who is versatile enough to be deployed in a bevvy of positions in the middle third.
He has played a key role in the resurgence of AC Milan this season, leaving Arsenal wondering what might have been had the player been persisted with and allowed some time to flourish at the club.
#2 Donyell Malen
After impressing with the youth teams at Arsenal where he scored goals galore, Dutch forward Donyell Malen earned his first professional contract at the club in 2016.
A year later, he made his debut for the club, albeit in a friendly, in Arsenal's 2017-18 pre-season win against Adelaide. But Malen was then sold off to PSV Eindhoven, without making a competitive appearance for the North London club.
Malen, a pacy player with impressing dribbling ability and goal-scoring prowess, has impressed with Eindhoven. Last sesaon, he scored all five in PSV's Eredivisie win over Vitesse.
He has scored 36 goals in 81 appearances in all competitions for the club, a tally that includes eight goals this season. Such has been the rise in stature of the 21-year-old that Arsenal are already bemoaning the loss of the prolific forward and are looking to bring him back to the Emirates.
Malen is being viewed by any to be the long-term successor of Pierre-Emerick Aubameyang, but it remains to be seen if the young forward opts to return to the club that once rejected him.
#1 Serge Gnabry
Serge Gnabry is easily the biggest name on this list of players who got away from Arsenal.
The German winger commenced his professional career at Arsenal in 2012 as a prodigious teenager but found first-team opportunities hard to come by as injuries stunted his progress at the club.
Nevertheless, in the few appearances he managed at Arsenal, Gnabry caught the attention of the club's then-manager Arsene Wenger, who lauded the player's versatility, creative prowess and ability on the ball.
"It's a fantastic opportunity for him. He can play right or left or even behind the striker. He can even play as a striker. He has the quality to be creative because he can dribble, he can run with the ball, he can be a good passer and he is a great finisher. On that front, once the confidence level (rises) he will be alright. His physical qualities, his technical qualities are at the requested level," said Wenger about Gnabry.
Gnabry was subsequently sold off to Werder Bremen before Bayern Munich came calling for his services in 2017. The player hasn't looked back since, evolving into one of the most sought-after wingers in the game.
He scored an impressive 23 goals in all competitions last season, helping Bayern Munich to the continental treble. Nine of those strikes came in the Champions League, with four alone coming at Tottenham Hotspur in a group-stage game.
On the cusp of his 100th appearance for the Bavarian giants, the former Arsenal player has already scored 40 times and provided 24 assists with the 25-year-old blazing down the right flank with devastating effect.
Arsenal can only think of what might have been had Serge Gnabry stayed on at the club.