Towards the end of a transfer window full of speculation, the Chile star came close to a move to Manchester City. Pep Guardiola's side agreed a £60 million fee with Arsenal, but the north London club's inability to sign Thomas Lemar from Monaco put an end to the deal.
Alexis, now in the final year of his contract, was understood to be furious with Arsenal after the deal collapsed on the final day of the window, and Guardiola has suggested City will return for him in January .
After an extended summer break, the ex-Barcelona star has featured just twice for the Emirates Stadium side this season - starting their 4-0 defeat to Liverpool and a 15-minute cameo against Bournemouth on Saturday between World Cup qualifying appearances for Chile.
And, while Wenger admits his star attacker was not ready to start in Saturday's win over Bournemouth, he denies claims the attacker is out of shape.
"On top of that Chile had a bad experience, but he came back full of desire and was ready to play.
"He is not fat. His fat percentage is under ten, so that’s not fat, but you know how it is when you don’t win, people find every problem for you.
"He was not completely physically ready to start three games in a week and certainly for Chile he was not completely ready as well."
Arsenal begin their Europa League campaign against Cologne this week, but the Frenchman is unsure if Sanchez will start.
"It’s a new experience for us," Wenger said.
"We will take it seriously, but as I said, the priority is to focus on the Premier League and as well to manage to combine the two until December and at least qualify."