'He had the scan two days ago and is out for a while, maybe two weeks or one more week but he's not available.
Despite all the reported interest in the Chilean from PSG and Manchester City, offers are yet to materialise, and Sanchez's wage demands are thought to have put off some suitors.
"He had a little abdominal strain that he caught on Sunday morning in training, before he came to Wembley (for the FA Community Shield final on Sunday)", Wenger was quoted as saying by Arsenal's website on Tuesday.
"I think he had in his career some bad moments because he had some small injuries", the Frenchman added.
Wenger said: "It was not easy to convince Ospina to stay, but he will play games and fight with Petr Cech to start. I don't know if it's two weeks, or one more week", Wenger told a news conference on Wednesday.
Wenger said Sanchez would not have started against Leicester even if he wasn't injured. "But all the other players prepared in preseason and are ready", Wenger said.
If Sanchez does not accept his new contract offer and the Gunners remain steadfast in their desire not to sell, then Arsenal risk losing him for nothing in the summer of 2018. It can happen in pre-season and anyway, I don't think I would have included him on Friday night.
"It's a long time since I spoke with Nasser because he was certainly very busy to complete the transfer of Neymar", Wenger said.
"(PSG) are looking for (Kylian) Mbappe, that's what I read in the papers. "I believe he will be a very great player".