The Chilean started the Gunners' game with Norwich, despite Wenger revealing that he had sustained a hamstring injury.
Wenger had already revealed that the Chilean was nursing a hamstring problem sustained in the Champions League victory against Dinamo Zagreb in midweek, so it was something of a surprise when he was included in the starting line-up for the clash at Carrow Road.
With an injury list at the club that is already alarming, it was much less of a surprise when the former Barcelona man had to be replaced early on in the second-half, after pulling up and holding the back of his leg.
His boss has subsequently placed the blame at Sanchez's door, having claimed that it was his decision to take to the pitch.
"I would have rested him but he said he was fine to play," he said.
As well as losing their key man, there are several reasons why the Gunners' trip to East Anglia may well be looked back upon as a crucial day in their season.
Centre-back Laurent Koscielny was also taken off with a hip problem, while Wenger also confirmed that Santi Cazorla sustained a knee injury (via BBC Sport). The Spaniard saw out the rest of the game as the away side had already made all three substitutions, which could well have aggravated the problem further.
With games against Sunderland, Aston Villa and Bournemouth ahead in December, the potential absence of three key players - as well as the six members of the first-team already out (via BBC Sport) - may make their task of keeping in touch with their Premier League title rivals an awful lot harder.