The Celtic boss has been discussing the 21-year-old defender.
Deila has come under fire from Celtic fans recently for selecting a number of different combinations in defence.
And that inconsistency cost the Scottish champions once again during their 3-1 defeat to Molde in the Europa League.
The Bhoys boss is quoted as telling reporters: "We lost Virgil [van Dijk] who was an important player for us. After that I brought in two players but Jozo Simunovic has been out for a while and Tyler is a young player coming up who we have had for a few weeks now and that is a positive.
"But things take time. It is not like buying somebody and we just put him in and everything is perfect. Jozo needs time to get to his best level but first of all he has to be injury-free.
"We have changed a lot in the back four and last year we had the record in the Scottish league for not conceding goals. That is a positive as well. We lost both centre-halves from last year and it takes a bit of time to replace them especially if we have players unavailable."
It's unclear whether Deila's reasoning actually makes sense, though, while the thinking behind his decisions can certainly be questioned.
Although he is now unpopular with some fans, former Celtic striker Chris Sutton believes the Bhoys boss doesn't rate Blackett and thereby doesn't start him.
It will be interesting to see who the Norwegian puts out against Dundee United, as well as during the rest of the Scottish champions' Europa League group stage.
Celtic sit bottom of Group A, a full five points behind Molde. A win against the Norwegian outfit at Parkhead will take them to within two points, while Fenerbahce are second on four points, with Ajax third - also on two alongside the Bhoys.