Shearer remains convinced Newcastle are good enough to survive, but he told the Mirror: "Kevin (Keegan) is not stupid enough not to know they have to improve and do so quickly otherwise they're going to be relegated.
"Everybody is slightly concerned, and I say slightly, because you have to be with the run of form they're in. I do think they have enough quality in the squad - although they may not be showing it at the moment - to get out of it.
"It's going to be tough. They're at Birmingham next Monday and if they don't get something, the pressure will mount and Fulham then becomes a must-win game."
Shearer added: "I think Kevin went into job with his eyes wide open. I spoke to him at the time and he knew it was a difficult run-in. There were a lot of things that weren't right behind the scenes and there was plenty to do, because that's why they got rid of the previous manager.
"I'm sure he thought they'd get better results, but they haven't.
"I'm convinced he'll get it right and I'm sure he'll get the time to get it right.
"People keep saying he has to change the team around, but there aren't enough players there to do that.
"I'm sure that was the biggest shock to him going in there, seeing the size of the squad. That's something he'll look at in the summer."