Celtic manager Ange Postecoglou says he has not "done a good enough job of convincing" the club's hierarchy of the need for squad reinforcements after their Champions League exit.
The Scottish Premiership side were beaten 3-2 on aggregate by Midtjylland in the second qualifying round, after losing 2-1 after extra-time in Denmark.
Postecoglou said that having an inexperienced side was not ideal.
"I still think it's my responsibility," he said after his second game.
"I'm the person that's been put in charge and if we haven't got players in obviously I haven't done a good enough job of convincing people we need to bring people in.
"I don't say that because I'm some kind of martyr, I just think that's my responsibility."
The average age of Celtic's starting XI for the second leg in Demark was just 23, with 18-year-old Dane Murray partnering 21-year-old Stephen Welsh at centre-back.
Despite taking the lead in the tie for the second time through captain Callum McGregor's brilliant volley, Celtic's defensive frailties were exposed twice as Midtjylland responded.
The club were unable to play new signings Carl Starfelt and Kyogo Furuhashi due to quarantine rules, and Postecoglou says the current group need more help.
"I've been trying to be as forceful as I can about what we need to bring in and the challenges we've had are well chronicled," the Australian added.
"Again maybe I wasn't clear enough - I don't know. I think I've been pretty consistent in saying that. We need more players in. The club's working hard to get those players in.
"Our supporters just want to see us bring the reinforcements in we need and I just need to keep reinforcing my views on it as strongly as I possibly can."
'It's going to get two years to get back' - reaction
Former Scotland forward James McFadden on BBC Radio Scotland
It's soul-destroying stuff for Celtic. They've made poor decisions at big moments. It's potentially a bigger rebuild than some people think. Not one player Celtic brought in last year strengthened the team.
Postecoglou made it clear that he has been asking for players and asking for reinforcements. He isn't getting them.
Former Celtic striker John Hartson on Premier Sports
Celtic are in a massive transition. The captain has gone and they have lost a load of key players. It's going to take two years to get back on track.
It depends what they give Ange. How much will Celtic back him? But he won't be given two years.
Former Celtic striker Chris Sutton on Premier Sports
Celtic are going to struggle to get into the Europa League. It is a building process.
[Chief executive] Dominic McKay should be apologising to Ange for the mess he has been left. This is a dreadful hand and this is not on the manager. He needs to turn it around in one year.
There have been issues needing addressed for a long time. [18-year-old defender] Dane Murray was thrown in at the deep end. It's embarrassing and mismanagement. This is on the board.