Sanchez has had to wear a protective face mask in recent weeks, but he accidently left in the dressing room at half-time at St. James’ Park.
The Colombian midfielder was then not focused for the first five minutes of the second period, as Villa’s coaching staff searched around to find it.
And Garde said: “I was not happy. It was a little sign that shows the fragility among the team.”
Sanchez has been handed a key role for Villa since Garde took charge, and he has played in their last five matches.
The French boss seemingly admires the 29-year-old’s battling qualities, and he has been tasked with protecting Villa's defence.
He performed the role fairly well against Newcastle at the weekend, as Villa managed to pick up a 1-1 draw.
The Claret and Blues went behind when Fabricio Coloccini struck from a corner, but they responded well in the second half and scored through Jordan Ayew.
The goal ensured that they picked up a deserved point from Tyneside, but it does little for their survival chances – as they are now 10 points away from safety.