The Chile forward was desperate to leave The Emirates this summer with Manchester City keen to get him our of north London.
But Arsenal insisted all summer he would not be sold and that proved to be the case.
Many are questioning Sanchez's commitment to the cause and a section of fans booed him as he came on from the bench in the 3-0 win over Bournemouth at the weekend.
Sanchez has less than a year left to run on his contract at Arsenal but Wenger is not concerned about his physical condition or mentality.
He said: "Yes, I spoke to him. He is focused, he told us he is focused on the Premier League and Europa League.
"On top of that he had a bad result with Chile against Bolivia, but he came back full of desire and ready to play.
“He was not completely physically ready to play three games in a week - and for Chile he was not completely ready.
“He is not fat. His fat percentage is under 10.
"You know how it is, when you do not win, people will find problems.”
Sanchez could feature on Thursday when Arsenal take on Cologne in the Europa League.
