Celtic had drawn the first leg of their Europa League last-32 tie against Inter Milan 3-3 and came to Italy knowing they realistically needed to win to progress to the next stage of the competition.
What would certainly help was a clean sheet - and that's exactly what the Bhoys managed right until the death.
But Virgil van Dijk's first-half sending changed the game in Inter's favour, with the Dutchman being sent off for two bookable offences.
Deila, however, felt the red card was 'very cheap' and believes the match official had a 'bad day' at the office.
Losing Van Dijk made life extremely difficult for Celtic and they represented British football with aplomb in the circumstances.
RD on red card and referee: "The sending off was very cheap. He had a bad day at work." #UEL (MH)— Celtic Football Club (@celticfc) February 26, 2015
RD on going down to 10 men: "It made it very difficult for us and we had to work very hard defensively." (MH)— Celtic Football Club (@celticfc) February 26, 2015
Celtic can now concentrate on domestic matters, as they can still win a treble in Scotland.
Key to those ambitions will be this Sunday afternoon's clash with second-placed Aberdeen, to be held at Celtic Park.
As for the Europa League, the Bhoys acquitted themselves exceptionally well and have the memory of two superb European nights that no one can take away from them. Not even the referee!