Paul Lambert reckons Celtic boss Ange Postecoglou looked "distraught" following the defeat to Bayer Leverkusen.
However, he laid the blame for the drubbing at the door of the players.
The Parkhead legend insists the team are hiding behind the manager as he blasted the Celtic Park dressing room in a scathing rant.
Defeat at the hands of the Bundesliga side leaves Celtic with an uphill battle to escape the Europa League group stage, but Lambert believes the problems run deeper.
The former captain believes his club are in danger of accepting being second best to Rangers going forward.
He told BT Sport: "Sometimes it's easy for the players to hide behind the manager, and I think that's what is happening with some of them.
"There is only so much a manager can do when he stands on that touch line. The players have got to win here.
"He looks distraught; that's the most I've seen him down in an interview, and rightly so.
"There has got to be a reaction up at Aberdeen on Sunday.
"For me the club is in danger of being on the peripheral. They could finishing second to Rangers, and say it's always nearly. They could not win a trophy; and he knows he has got to win a trophy here.
"But you can't keep hiding behind the manager. Some of the players will have to step up and this certainly isn't good enough to be losing 4-0 to Bayer Leverkusen. "
