The forward has been in blistering form for the Scottish Premiership leaders this term.
The Scotland international is the Hoops' top goalscorer this term, having already scored 34 goals from just 41 appearances in all competitions. And while Deila insisted that he is not shocked by the fact that Griffiths has been in stunning form for the whole campaign, he did concede that he has been taken aback by just how ruthless the forward has been.
"I always felt that he would be able to hit the 30-goal a season mark," he told the Evening Times.
"But he really turned things around. His whole attitude and approach is different and he has had his rewards for that.
"He has surprised me but his ability has not been a surprise. I am pleased for him."
Although the amount of game-time that Griffiths has enjoyed in the sole-striker role means that it was always going to be highly unlikely that anyone else was going to top the goalscoring charts for the Bhoys, there is such daylight between himself and the next most prolific goalscorer that it is safe to say that Celtic's season would be coming under greater scrutiny if it wasn't for him.
If he was not in the side for whatever reason, it is difficult to imagine that the likes of Anthony Stokes, Nadir Ciftci - both of whom have now left Parkhead on loan - Colin Kazim Richards and Carlton Cole would be able to contribute the same amount of goals collectively as what Griffiths has managed on his own.
And with Deila still coming under fire despite the 25-year-old's goals, the side's fortunes if Griffiths had not been as clinical as he has been may have made the calls for the Norwegian's sacking too loud for the club's hierarchy to ignore.