The Bhoys forward was speaking to reporters after the Scottish Cup semi-final.
Celtic striker Leigh Griffiths has revealed that Inverness Caledonian Thistle defender Josh Meekings admitted to him that the ball had hit him '100 per cent' on the hand during his goal-line clearance on Sunday afternoon, according to the Glasgow Evening Times.
Celtic and Inverness were contesting a Scottish Cup semi-final at Hampden Park, with the latter defeating the Bhoys 3-2.
But a key moment came when Griffiths aimed at goal but had his shot blocked by Meekings on the line - with his hand.
An understandably disappointed Griffiths said: "It's one big decision that has changed the game for us. Everyone will tell you the same. You would need to ask the referee and the assistant behind the goal whey they thought it wasn't a penalty.
"I asked the centre-half during the game if it hit his hand or his face and he said 'hand, 100 per cent'."
Deila had earlier expressed his dismay at another poor decision going against Celtic this season as the Scottish champions' treble dreams died for another year.
The last time Celtic completed the feat was in 2001 and the poor refereeing decision certainly played a big part in preventing them from achieving it once again.
The Norwegian admitted his players were 'angry' and joked that Scottish football should have seven referees at matches instead of five.
Celtic's sole focus now remains the Scottish Premiership. Wouldn't it be ironic if another poor decision or two cost them there between now and the end of the season?