Celtic went into their Champions League group stage encounter as underdogs but hoping to spring a surprise on Leipzig.
The Germans took the lead though in just the 27th minute when Christopher Nkunku found the back of the net, but Celtic drew level just minutes into the second half when Jota struck.
A Joe Hart error however handed Leipzig the lead back as Andre Silva scored, while the Germans then took a two-goal advantage when the Portuguese grabbed his second after a slick move.
Celtic have now collected just a single point from their three Champions League group games and former Dundee boss Duffy feels they were just too open in Germany.
“You can’t be that open in Champions League football”, he said on BBC Sportsound.
“It’s entertaining, but away from home in Europe, you need to put the brakes on a little bit.”
Duffy also admitted that the mistake made by goalkeeper Hart during the match was key to the Bhoys’ loss.
“The error from Hart is critical.
“Celtic had just got away with the disallowed goal – they’d been given a lifeline.
“You can’t make mistakes at a time like that.”
Celtic are next in Champions League action at home against Leipzig next week and the pressure is on for Ange Postecoglou’s men to pick up all three points.
