Manager Ronny Deila insists Celtic will "rise up" following their disappointing exit from the Champions League.
Deila's side were knocked out at the third qualifying round stage as Legia Warsaw won 2-0 at Murrayfield to complete a 6-1 aggregate win.
"We didn't play as a Champions League team," Deila told BBC Radio Scotland. "We have to perform much better than that. We have to win the league."
Celtic will now go into Friday's draw for the Europa League play-off round.
And by missing out on the group stages of the Champions League, Celtic will not gain the £14m they took in from last year's campaign, having pocketed almost £19m in prize money the season before.
Deila's men never got going against the Polish champions and the Norwegian admitted his players were well short of the standard they need to be at that level.
"It was not good enough," he said. "They got two easy goals, again, and that's worrying me. We just have to say we lost to the better team. The boys want to play better.
"We are very disappointed. We're going to rise up and we're going to perform much better, win the league again, and next year in this situation we're going to go through.
"We're going to do everything to get into the Europa League. It's a fantastic chance to play against European opponents and that's what we need now."
Deila was locked in the dressing room for some time after the game, but afterwards refused to blame his players and instead took full responsibility, insisting a different line-up would not have changed the result.
"We know there's much more in this team and there's a lot more to fight for this season," he explained.
"Maybe we could've done things differently but I don't think we would've won this game."
And, when asked about the search for new recruits, he replied: "We're working on that all the time so of course we want to make the team better."
Addressing his post-match media conference, Deila continued: "We need players with pace, ambition and who are young. I want to build a team who could last for many years."