The Scottish champions had been reinstated into the competition after Legia Warsaw fielded an ineligible player in their 6-1 aggregate win over the Hoops in the previous round.The 1-0 play-off defeat by Maribor at Parkhead on Tuesday night took the visitors into the group stages of European football's premier club competition, 2-1 on aggregate.However, Maribor skipper Tavares grabbed the crucial goal in the 75th minute which could cost the Parkhead club up to £20m in lost revenue.Celtic drop into the Europa League but that will do little to enthuse Hoops fans who vented their anger at the final whistle with some protesting outside the main door.Celtic boss Ronny Deila admitted his side was "not good enough".Deila, who took over from Neil Lennon in June, said: "The first half wasn't good enough, we were more aggressive in the second half and it was a very even game."They had two chances before the goal came and they were more effective."At the end, there is only one thing to say, we haven't been good enough and we haven't deserved to go to the Champions League."There is no excuse. We are not good enough. Now it is the Europa League and we will do everything we can to achieve things in that competition."That is our level now and that is what we have to work from."We didn't lose because of the defending, we lost because we didn't create anything."We have to have more tempo and movement in our play, that is the job and it has to start now."