The Hoops boss said he was expecting his team to win the game, but admitted that their attacking was poor throughout the evening.
"Attacking-wise first half was very disappointing for us. Although, James Forrest was a stand out," BBC Sport quotes him as saying.
"I was expecting to win the game and I'm bitterly disappointed. Our attacking play was insipid in the first half and marginally better in the second.
"People keep coming to me wanting to play games but when [Gary] Hooper comes on we open them up at will. Another basic error has cost us."