The former European champions won 2-0 but Leigh Griffiths missed the late spot-kick that would have ensured a much more comfortable margin for the second leg in Reykjavik after Stefan Johansen and Griffiths argued over who should take it.
"It is Leigh Griffiths who takes the penalties, it should be very clear," Deila told reporters. "There is nothing professional about it. We shouldn't fight about who takes a penalty.
"Of course it impacts on the taker, it gives extra pressure to him. The longer you have to wait, the more chance you have to miss it.
"3-0 is a totally different result to 2-0, so it's disappointing."
(Reporting by Steve Tongue; editing by Sudipto Ganguly)
Share
