Oxlade-Chamberlain, 22, scored a superb individual goal as Arsenal beat Chivas de Guadalajara 3-1 on their pre-season tour in the United States.
Chuba Akpom and centre-back Rob Holding, who joined from Bolton in July, also scored in Los Angeles.
"It's a very important season for him," Wenger told the Arsenal website.
"He has been out for a long, long time."
The England international, capped 24 times, injured his knee during the Champions League loss to Barcelona on 23 February.
He played 70 minutes of Sunday's match at the StubHub Center, following 45 minutes against the MLS All Stars in Thursday's 2-1 win.
Wenger said Oxlade-Chamberlain gave the team "power and penetration".
The Gunners boss added: "He has it all. That's why I would like him to get to the level he can go to.
"Maybe he doesn't completely believe himself how good he can be and that's the final step for him."
Arsenal conclude their pre-season schedule with a friendly against Manchester City in Gothenburg on Sunday.
A week later, they begin their Premier League season at home to Liverpool.
Alex Oxlade-Chamberlain faces an "important" season after overcoming the knee injury which kept him out of Euro 2016, says Arsenal boss Arsene Wenger.