But Gooners shouldn't be overly concerned. Gabriel, even at 24, is far from the finished article - particularly at Premier League level.
His Gunners career could mirror what he experienced at Villarreal, where coach Marcelino, after quickly realising Gabriel was some way from La Liga standard, took the signing from Vitoria under his wing and with personal coaching was able to build the defender's game to the point where he is now one of the Yellow Submarine's richest ever transfers.
His first season was a slow burn. While an exceptional athlete and, as highlighted by Arsenal boss Arsene Wenger, boasting great composure on the ball, there were doubts about his ability to get the better of strikers in the Spanish Liga.
"That first season was all new to me," recalled Gabriel last year. "It was a year of adjustment and not much more. It was a major change for me, but the training helped me to adapt and I'm now more comfortable at this level."
That "training" Gabriel mentions was dominated by one-on-one sessions with Marcelino, who, in that first 12 months of the Brazilian's European career was determined to get him to the required level.
Throughout season 2013/14, local scribes would report on training sessions punctured by the badgering of Marcelino towards Gabriel. He never let up on the young defender, pushing him for greater focus and awareness of opposition players around him.
As Wenger appears to be doing now, Marcelino refused to rush Gabriel into his line-up.
"That first game took a while to arrive," said the defender, "but the team was doing well and I still had to learn.
"The debut was tough! I was not used to the game's pace and I was always having to think about how to react next. There are some great players in this Liga and you cannot drop your concentration. You have to keep up with them."
Gabriel admits the management of Marcelino has been crucial in his improvement.
"Marcelino was always watching me at training. He's given me great support and always assured me when I was ready, I would get my chance. I never dropped my head, I always kept at my work and effort.
"He'd always talk to me about what I needed to improve. That was important, because I needed to know what had to be improved so I could adapt as quickly as possible."
The game hasn't come easy for Gabriel. Coming through at Vitoria, he experienced both relegation and promotion with the Bahia giants - and also clashed physically with home fans. But for his work ethic and devotion to Vitoria, he remains popular at home.
"He'll never change his attitude, his commitment," says former teammate and Vitoria goalkeeper Wilson.
"We know Gabriel and know his character, dedication and affection he has for the club (Vitoria).
"Going abroad has benefited him professionally. It's only a matter of time before he plays for the Selecao."
For Marcelino, Gabriel represented a personal undertaking - and to see him sold, even if it was for almost €20 million - generated feelings of a job not yet complete.
"The departure of Gabriel surprised us all because we did not expect to make changes to the squad," the Villarreal coach lamented.
"From a sporting point of view, it is unfortunate, but it was an irresistible offer from Arsenal for the club and to the player himself."
Now it's over to Wenger, Steve Bould and the Gunners coaching staff to pick up where Marcelino left off with the Gabriel project.