Former Arsenal captain Gilberto feels the club 'made a mistake' by allowing experienced players to leave the Emirates.
Gilberto's six-year stay in North London came to an end last summer after he was sold to Greek side Panathinaikos.
Gunners boss Arsene Wenger also saw midfielders Mathieu Flamini and Alexander Hleb depart, as he planned to allow his youthful players to flourish.
However, the side have struggled his term, and they risk losing out on UEFA Champions League qualification following the emergence of Aston Villa.
Gilberto, 32, is of the belief that Arsenal are currently paying the price for a lack of experience amongst their ranks, although he is hopeful they will improve as the term progresses.
He said in the Evening Standard: "I never fell out with Arsene, whatever people say. I had to respect his decision even if I disagreed with it.
"We had good conversations but, when it came to talking about whether he still saw me as part of the team, it wasn't the conversation I expected.
"Maybe, I thought, it was time to leave Arsenal. I understood what the manager's idea was; he had so many good young players and, if I was in the team, they wouldn't have the chance to develop."
He continued: "It's only my opinion, and I could be proved wrong, but I think Arsenal made a mistake letting some of the more experienced players go.
"It would be good for the development of the younger players. They're having to learn for themselves and that's hard.
"These players need to find that killer instinct. They can get there but it takes time. I hope it comes quickly."