He had a scan on Monday, which revealed the extent of the damage, and revealed that he will not be fit to play against Leicester City in tomorrow's English Premier League season opener, and Stoke City the following weekend.
The Frenchman has remained unmoved in his stance over Sanchez's future and said the versatile forward will have to "respect" his decision to keep him in the capital. A lot was created by my own situation.
Sanchez was in the stands for Arsenal's Community Shield shootout win over Chelsea on Sunday, having returned to London Colney to catch up on training. Overall I believe that it's down to us. "The trend has always to come from the team".
Arsenal could have up to 11 first team players unavailable on Friday.
Arsenal could be playing the attacking option this season by placing Lacazette in centre stage up front with Sanchez and the other possible signing Lemar.
When Benitez committed to stay at Newcastle at the end of last season he was promised "every last penny" by club owner Mike Ashley to invest in the squad, but the reality has not been so simple.
The match program for Sunday's Community Shield at Wembley showed Chelsea listing 17 fewer players than opponents Arsenal.More news: S&P closes barely lower despite North Korea tensions
Key Player: Alexandre Lacazette - There is pressure on Arsenal's marquee signing to score the goals to push them towards the title.
The 26-year-old set Arsenal back an initial fee of £46.5 million ($60.3 million, 51.5 million euros) and is expected to lead the line, flanked by Sanchez and Ozil.
And it's an intriguing one in many ways with the Top 6 sides all potentially capable of winning the title or missing out on the Top 4.
Riyad Mahrez, who has been linked with Arsenal and Roma, wants to leave the Foxes but Shakespeare says he won't be allowed to go "until we get a reasonable offer".
The link drawn between Wenger regarding the possibility of a female manager in the Premier League and managers who are not "football specialists" is an interesting one, but perhaps let's not dwell on what we're sure was a perfectly innocent segue.