Former Celtic star Roy Keane is of the opinion that a 7-0 loss should be unacceptable for the Hoops.
The Scottish champions qualified for the group stage of the Champions league for the first time in two years this season, but Brendan Rodgers’ side were dished out a 7-0 hammering by Barcelona in their first group game.
Celtic edged out Israeli outfit Hapoel Be'er Sheva 5-4 on aggregate in the final qualification round to book their place in the group stage of the Champions League last month before celebrating wildly to mark the occasion.
And Keane, who played down Celtic’s 5-1 win in the Old Firm derby over Rangers last weekend, thinks his former employers need to change their mindset if they wish to do better in Europe.
"I just think they need to do a lot better in Europe. It's easier said than done of course and this time it's obviously difficult with the group they are in”, he said on STV's Champions League highlights show.
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"The whole mindset has to change and don't accept particularly away from home being the whipping boys of Europe.
"They've got to change the mindset. I'm on about the qualifying games when they were scraping through then celebrating like they'd won the bloody thing.
"On one hand we're being told Celtic are a great club, great tradition, great history and they go and lose 7-0 to Barcelona and people are almost saying 'these things happen it's acceptable'.
"The previous weekend they won 5-1 against one of the worst Rangers teams I've seen in a long time."
Celtic’s other two opponents in Group C are Manchester City and Borussia Monchengladbach, with the Hoops scheduled to face the Citizens in their next Champions League match on 28th September.
