The 20-year-old England international has fought his way back from a series of problems that sidelined him for the whole of last season.
He produced an all-action display at the heart of the Arsenal team in Saturday's 2-0 win over West Brom at Emirates Stadium and Wenger has been buoyed by his return to a beleaguered side.
"This is the first time I see him very, very close to the player he is," Wenger said of his performance against West Brom.
"We have to see if he has no reaction. It was good to leave at home in midweek (for the Champions League tie at Olympiakos) to give him a breather from time to time.
"But when he plays at that level, and you are under the pressure we are under to win the games, it is difficult to leave him out.
"Jack analyses his game well and is very demanding with himself, he works hard in training.
"The surprising thing for me is that he is (ahead of schedule). I expected him to be back at his best next year, in February. He looks (almost back to his best) much earlier than I expected him to be.