The Chilean international - along with defender Shkodran Mustafi - was among the last two players to return to pre-season training after his exertions at the Confederations Cup and a subsequent bout of flu.
Sanchez eventually rejoined his teammates on 1 August following the Emirates Cup tournament but sat out the Community Shield victory over Chelsea last weekend with Wenger stressing that he was "short of preparation".
The 28-year-old appeared to face a race against time to be fit for Friday night's (11 August) Premier League curtain-raiser against Leicester City. However, Wenger has now revealed that he will definitely miss that game and probably also sit out the trip to Stoke City eight days later.
"He had a little abdominal strain that he caught on Sunday morning in training, before he came to Wembley," he told reporters at pre-match press conference held on Wednesday morning. "He had a scan two days ago and he's out for a while - we don't know if it is two weeks or one more week, but he will not be available. We think he will not play at Stoke."
He added: "For us Alexis Sanchez is a loss, of course. But we have all the other players prepared in pre-season and they are all ready. It can happen in pre-season and anyway, I don't think I would have included him on Friday night. I don't think I would have started him. He is focused. Of course when you have treatment on a medical bench, it's not easy."
Arsenal were without Santi Cazorla, Gabriel Paulista, Francis Coquelin and Jack Wilshere for Sunday's defeat of Chelsea, while Aaron Ramsey (calf) and Mesut Ozil (ankle) also missed out along with Mustafi. Captain Per Mertesacker, meanwhile, had to be withdrawn after just 32 minutes due to a bloody gash over his right eye sustained during an accidental collision with Gary Cahill.
Speaking after that latest clash with the defending top-flight champions, Wenger, who will not be able to call upon the services of the suspended Laurent Koscielny, said that Ozil only had a "little chance" to feature against the Foxes and that Ramsey could also be lacking the requisite fitness.
The Frenchman was coy on the rest of his injury concerns two days away from Leicester, stating: "I have plenty of uncertainties about the players who didn't play against Chelsea. For example Ramsey, Ozil, Mertesacker... and of course Koscielny is suspended.
"I have players coming back who have not played, like Mustafi. Alexis will not be available for example, so I cannot go into the game with too many uncertainties. I can take a gamble on one, maybe maximum two, but I focus more on the players who had the right number of competitive minutes in recent weeks."