Stefan Johansen admits Celtic "threw away" their chance of reaching the Champions League group stage.
A 1-0 win for NK Maribor in Glasgow on Tuesday gave the Slovenian side a 2-1 aggregate win and consigned Celtic to the Europa League group stage.
"It's sad, tough and very disappointing," said 23-year-old Norway international Johansen.
"We wanted to go out and control the game and create chances but we didn't manage to do that."
Marcos Tavares struck with 15 minutes of the second leg to play, cancelling out Celtic's away goal from the first leg and forcing Ronny Deila's side to chase a goal to level the tie and force extra-time.
Callum McGregor, who scored in last week's draw in Slovenia, fired against the crossbar before the Tavares goal and Efe Ambrose headed a chance to equalise wide of the Maribor goal before Virgil van Dijk drew a save from visiting goalkeeper Jasmin Handanovic.
Afterwards, Deila admitted Celtic had not been good enough but Johansen insists his manager and countryman is not to blame for Celtic's play-off defeat.
"Ronny has made it clear what he wants but of course it will take time," explained the midfielder.
"Of course he's disappointed, He's going to bounce back and he's going to be a successful Celtic coach.
"We had a good chance to go to the group stage but we just threw it away.
"We need to improve as a team and as players. That's what we're going to work on."
The tie with Maribor was Celtic's second chance to reach the group stage of the Champions League after they were reinstated into the competition. Their second-leg defeat by Legia Warsaw in the previous round was reversed to a 3-0 win after the Poles fielded a suspended player in the last few minutes, resulting in an away goals win for Celtic.
And Johansen's international team-mate Jo Inge Berget, who recently moved to Glasgow on loan from Cardiff City is eager for Celtic to return to the Champions League next season.
"This is not what we wanted and not the way we wanted to play so, of course we feel down now," said the 23-year-old
"We've still got a lot things to play for and we need to win the league to get a chance to prove ourselves next year in the Champions League."