The Magpies are currently 18th in the Premier League and are yet to win this season.
Shearer told The Chronicle: "It has been poor since January this year. The quicker we can get out of it the better. I don't hold too much hope for us this season. I think it could be a long hard season for us.
"You can make whatever excuses you want - injuries, too many games or confidence. Put all of that to one side, the simple fact of the matter is we just have not been good enough.
"It's simple. That's the harsh reality of it. Things have to improve and they have to improve pretty quickly or we could find ourselves in a hole."
Newcastle host Leicester City after the international break.