The Gunners have not won a trophy since the 2005 FA Cup and this season have dropped to 10th on the Premier League table, prompting Robson to call for a change in management, which he also wanted about four years ago.
The 48-year old told talkSPORT that the Frenchman's coaching style has the Arsenal side under-prepared.
"I would have sacked him four years ago but I'm in the minority. Arsenal need a new manager and they need it soon," Robson said.
"In my view he's not (unsackable). I wrote an article about four or five years ago when I said he was the cause of a lot of problems at Arsenal.
"He doesn't have the tactical understanding, his manner on the side of the pitch doesn't help the team, he's petulant and therefore his players become petulant. He doesn't give any information from the sidelines and his teams look under-prepared defensively.
"I wrote that article five years ago and nothing has changed my mind since. In fact, my views on Arsene Wenger are even stronger now than they were then. There's still 50 per cent of the fans which will say what a good job he is doing and we must trust in Arsene Wenger but I just don't see it."