The Norwegian has been discussing his side's pre-season loss.
Celtic boss Ronny Deila has assured fans that the mistakes on show against Dukla Prague during their friendly defeat won't be repeated once his first team are sharper, according to the club's official Twitter feed.
Celtic lost 5-3 to Dukla Prague, with some putting in a disappointing performance - in contrast to their recent 2-0 friendly win over Den Bosch.
But Deila has promised his side's supporters the things that went wrong against the Czech side are nothing to worry about, as the mistakes simply wouldn't happen with his Celtic squad fully fit and match-ready.
RD: "We met a good team today and had a good test. We have a lot of things to work on." (MH)— Celtic Football Club (@celticfc) July 4, 2015
RD: "But there are a lot of things you just have to forget as you know when the sharpness returns we won't have situations like today." (MH)— Celtic Football Club (@celticfc) July 4, 2015
A number of Bhoys stars returned to the fold for this friendly and it was Leigh Griffiths who netted Celtic's first goal.
Gary Mackay-Steven then scored Celtic's second, before Virgil van Dijk added a third.
The biggest positive, of course, will be the game time for many, as opposed to the result and perhaps performance levels against Dukla Prague.
Deila also credited Prague's win to their players having played more games than the Hoops. Next up for Celtic in pre-season are David Moyes' Real Sociedad side.