Shearer, who scored 148 goals in 303 games for his hometown club, has also criticised the club's transfer policy following the sale of Yohan Cabaye in January.
"At the minute they're in the relegation zone because they deserve to be there. They haven't defended well enough, they haven't scored enough goals and that's a recipe for disaster when that happens," Shearer told talkSPORT.
"If you speak to anyone in football, they would never ask for anyone to lose their job or be sacked. But, we all know that football is a results business and Newcastle haven't had enough since January.
"It doesn't help that you're constantly selling your best players over the last few years. It can't keep happening that you hope to survive by selling your best and then buying cheaper players in. It doesn't work like that unfortunately."
Newcastle United currently sit 18th in the Premier League with four points from seven games this season.