It was clear he had talent, that had been evident since he broke through as a youngster and made his debut in 2008.
But he never quite broke through into the first team, and by time he left this summer, he was well down the pecking order.
The Mexican international is still only 23, but spent the last 18 months of his Gunners spell out on loan with West Brom and then Real Sociedad.
Arsene Wenger gave up on trying to persuade the talented attacker to bide his time in the club's queue for places, and allowed him to leave for Sociedad this summer for just £3.5 million.
The league leaders showed they were no 'Invincibles' when a 90th minute goal from Imanol Agirretxe clinched a 3-2 victory for Real Sociedad.
Vela was a thorn in Barcelona's side the entire game, playing in the middle of an attacking three in a 4-2-3-1 formation, and found himself fouled more times than any other player on the pitch.
It was Vela whose run and cross provided the opportunity for Chory Castro to score his side's opening goal, inspiring their fightback from going 2-0 down after 25 minutes.
It meant Sociedad went in at the break 2-1 down, and had a platform to build on in the second half, which they did, via their injury time winner.
Vela has been quite the catch in La Liga this season; in 19 games he has scored 8 goals and provided 5 assists.
Arsenal fans may well wonder how Andrei Arshavin remains playing for their club and Vela was allowed to leave; but unlike Arshavin, Vela is wanted elsewhere, shows an excellent attitude, and his best years are ahead of him.
How good can Vela become? Should Arsenal have persisted with him?