Austin believes the Reds should have acted quicker to fill the void at the back.
But Austin doesn't understand why Liverpool waiting until the final day of the transfer window to snap up the defenders.
"They've got a long list of injuries – I get that, I do – but that is part of football," Austin told talkSPORT. "Van Dijk has a massive injury in November, and they know he's out for the season, and it takes them until deadline day to try and replace him?
"You can't replace him, but to bring in someone that can fill the void… I'm not sure they've been able to do that."
He added: "Second season syndrome… you usually say that about promoted teams, that they do well the first year but the second year they fail.
"Hang on a minute, Liverpool are doing it here.
"Me being a Liverpool fan, it was fantastic last year. I was thinking, 'Come on, let's back it up and go on a run of two/three/four/five years like United did.
"But it's just not happened. And at the moment it's going to be a struggle for top four… it's going to be a struggle for top six!"