Celtic manager Ronny Deila admitted two of his players squabbling over who should take a penalty in the 2-0 win over Stjarnan was "unprofessional".
Stefan Johansen and Leigh Griffiths argued about the spot-kick before the latter's attempt was saved.
Earlier, goals by debutant Dedryck Boyata and Johansen put Celtic in command of the Champions League second qualifying round tie.
And Deila said it was "very clear" Griffiths was to take the penalty.
Asked what had transpired on the pitch, Deila replied: "I don't know, I have to ask them.
"It's very clear who's going to take that penalty; the guy who took the penalty.
"Leigh has taken penalties before so that is quite clear. We can't have it like that, it's unprofessional."
Boyata headed Celtic in front near the end of a first half dominated by the hosts. Johansen, who had set up the opener from a corner, converted Stuart Armstrong's pass for Celtic's second after the break.
"We created a lot of chances, we should've scored more goals but 2-0 is a good result and that should be enough when we get up to Iceland," Deila told BBC Radio Scotland.
"We had five big chances in the first half, we should have at least one more goal there. I think we had opportunities to kill the game but that's football. I'm very happy that we didn't concede anything."
Meanwhile, Deila revealed winger Gary Mackay-Steven had been replaced in the starting line-up by James Forrest shortly before kick-off due to a groin strain.
"We don't take any chances," said the Norwegian. "We had to let him rest."
Boyata was withdrawn late on and later revealed he had cramp.
"For myself, it's something I'm not happy with," said the former Manchester City player. "I wanted to finish the game.
"It's not put me in a good mood and hopefully it's something I can sort out very quickly."