Shearer has questioned the attitude of the players after another poor performance this season.
"I don't like the attitude of several of Newcastle's players," Shearer said on Match of the Day.
"You can't just turn up in the big home games, they drew with Liverpool, drew with (Manchester) City, they beat Spurs, they beat Chelsea, they beat Arsenal.
"They were dreadful defensively, Thiago's too strong and bullies Fabian Schar. I look at Lewis Hall with his hands behind his back, he's not even in the box, how are you expected to twist and turn?
"Harvey Barnes makes an error. OK, it's a really poor pass but look at the defending. Fabian Schar has got to engage at some point, he's got to try to tackle him.
"Dan Burn's trying to get back, he's screaming to him (Schar) push him on the outside but he never gets near him, he (Yoan Wissa) gets a free shot.
"You've got to at some stage tackle him.
"This is worrying, because two years ago we were praising Newcastle all the time for their energy, for their closing down, for their pressing, there was none of it.
"No one gets within five yards of any Brentford player, now all of a sudden they're in Newcastle's final third, still no one within five, 10 yards of anyone. That's not good enough, that's not acceptable, that's why they got beaten today."