The Black Cats were beaten 3-1 by Barclays Premier League newcomers Norwich at the Stadium of Light to leave Advocaat scratching his head and disgruntled supporters urging chairman Ellis Short to invest heavily in the remaining weeks of the summer transfer window.
Advocaat, who will hold a grisly post-mortem on Sunday, said: "Even this squad must be good enough to get a better result against Norwich with five new players, but there is something wrong, that's quite simple.
"I have an idea about it, but tomorrow we will have a meeting and they can talk and I will talk.
"What was so wrong was I saw players playing - and I don't want to mention names, it was the whole team with the exception of one or two players - and they did things that I don't expect from a player at this level.
"I have to know why that can happen because it's really strange for me. You can play badly and badly, but not knowing what to do is even worse."
Rumours suggest the Dutchman will walk away from the job and retire.