Toon chiefs have missed out on a raft of big-name transfer targets, while also battling to convince Alexander Isak to stay.
Shearer said in his BBC Sport column: "So far, Newcastle's pre-season has been a nightmare. There is no other way of describing it.
"They have had a disastrous transfer window, missing out on every one of their top targets they went for, and on top of that they have got Alexander Isak's situation hanging over them as they get ready for the opening weekend."
He added: "Newcastle went into the summer with no chief executive or sporting director, which I find amazing. They knew Darren Eales was stepping down as chief executive last September - 11 months ago - and Paul Mitchell left as sporting director at the end of June.
"I don't know why they haven't appointed anyone yet or if that has hindered them in the transfer market, because I am not inside the club, but from the outside it is not a good look.
"It's a mess, and it begs the question about who has making the big decisions."