The Bhoys boss was thrilled with the 22-year-old's display.
What he might have been more surprised by on Wednesday night, however, was exactly who he was discussing. Indeed, Deila feels Tom Rogic was 'excellent' during Celtic's 2-0 friendly win over Den Bosch, according to the club's official Twitter feed.
So confident did Deila sound, though, that he didn't seem surprised at all.
In fact, the Celtic boss says he has been expecting this kind of display from the 22-year-old ever since he was brought to Parkhead.
RD on Tom Rogic: He's a great player and a great person. He works really hard and has been very unlucky with injuries in the last year.— Celtic Football Club (@celticfc) July 1, 2015
RD: Now we have control over his body and you can see what kind of player he is.— Celtic Football Club (@celticfc) July 1, 2015
RD: There's a reason why he got brought to Celtic and he's very hungry to show what is in him.— Celtic Football Club (@celticfc) July 1, 2015
Deila was full of praise for several Bhoys and this was solid preparation for the Scottish champions' upcoming Champions League qualifiers.
But it was clear Rogic caught the eye of the manager especially and the Celtic boss was delighted with the midfielder's speed - something he feels will improve even further with more training.
RD: Today he played excellent and you can see he's so good at scanning and getting his touch forward.— Celtic Football Club (@celticfc) July 1, 2015
RD: He looked very quick today as well and his footwork is getting better every day. He's going to improve with more training.— Celtic Football Club (@celticfc) July 1, 2015
Others on show against Den Bosch were debutant Dedryck Boyata, as well as returning Bhoy Liam Henderson. Deila is clearly taking the opportunity to watch absolutely everyone at his disposal.