Deila on Charlie Mulgrew
Mulgrew replaced Tom Rogic in the 66th minute but walked off down the tunnel 21 minutes later when Vaclav Cerny put the Dutch side 2-1 in front.
After two months out injured the 29-year-old was drafted back into the squad due to injuries and suspensions as Celtic looked for the win they needed to keep alive their qualification hopes.
The sight of Mulgrew walking straight off the pitch puzzled fans at the match as well as television viewers but Delia explained that the player was better off in the treatment room than on the pitch.
“He pulled his muscle again,” the Celtic boss said. “ I don’t know if it is the same injury again. It seemed more advanced than just a cramp. When you can’t run, it’s better he is not there.”
Looking at ways of improving his side Deila added: “We buy talent, players who can be Champions League players. Nobody comes in and is a Champions League players the first game.
“You have to develop them through time and we are going to be ready next year, that is the message to all the fans and that is the task that I and everyone in this club has.
“It is small details, you have to be good in small details to win games. That is very close but it is not good enough right now. I see it small details. If you see the big picture you are also going to see that.
“It is very hard to bring in a player who has played a lot of Champions League games, that is different level but we have created a lot of Champions League players and we are going to do that in the future as well.
“It is important that we use the January transfer window well and the summer one as well of course.”