The former Magpies skipper feels Saturday's 3-2 defeat to Swansea at St James' Park was a tipping point and he is genuinely worried about their chances of being caught by the clubs below them.
Newcastle currently sit 14th with 35 points, five ahead of rivals Sunderland in 18th with four games to go, but they are in the middle of a wretched run of form having lost seven on the bounce.
"Have no doubts about it - Newcastle are now in real danger of going down," Shearer wrote in his column in The Sun.
"I didn't think so until Saturday but after that performance I can't actually say with any certainty that we will get another point this season."
Newcastle 2 - 3 Swansea
Newcastle 1 - 3 Tottenham
Liverpool 2 - 0 Newcastle
S'land 1 - 0 Newcastle
Newcastle 1 - 2 Arsenal
Everton 3 - 0 Newcastle
Newcastle 0 - 1 Man Utd
The 44-year-old lays the blame firmly on the players, lamenting their attitude and expressed sympathy for head coach John Carver as he tries to get more from them.
He added: "Carver himself has been getting some stick. But he loves the club and I know he is hurting.
"Why don't the Newcastle players start taking some responsibility? Because right now they are an embarrassment."
Shearer has been impressed by Aston Villa's resurgence, Leicester's remarkable four-game winning streak and feels Hull will be buoyed by their win over Palace at the weekend.
He feels all those sides can overhaul the Magpies and just questioned if Sunderland can get the points they need to drag Newcastle deeper into the mire.