The Republic of Ireland assistant manager was critical of Celtic players for their excessive celebrations after defeating Israeli club Hapoel Be'er Sheva in the Champions League play-offs last month.
Keane claimed that the Bhoys celebrated their play-off triumph like they were playing for a small club like Altrincham, and their joy at simply qualifying for Europe's top flight club competition was quickly distinguished when they were hammered by Barcelona on Tuesday night.
The former midfielder was speaking after Celtic's embarrassing 7-0 defeat to the Catalan giants.
"Even when they qualified for this group, the celebrations were way over the top," he told ITV.
"They scraped through and I thought they'd actually won the competition.
"People were hugging each other - the manager, the coaches, the players. They should be expecting to do well in this group.
"Throughout the last number of years when they have been involved in Europe they have struggled, and lesser teams than Celtic have done well in Europe.