Kris Commons believes Celtic paid the price in the Champions League for not replacing Gary Hooper with another top-class striker.
The Hoops midfielder was speaking after the 6-1 thrashing by Barcelona at the Nou Camp on Wednesday night saw the Scottish champions finish bottom of Group H with three points, leaving them without the prospect of European football in the new year.
After top scorer Hooper moved to Norwich City in the summer, Celtic added Teemu Pukki and Amido Balde to their attacking options alongside Anthony Stokes but it is Commons who is the most prolific this season with 12 goals in 21 games.
The 30-year-old was surprisingly dropped to the bench against Barca, where Georgios Samaras's late consolation goal was only Celtic's third in six group games.
The former Nottingham Forest and Derby player believes the Parkhead club needed to bite the financial bullet to replace Hooper.
He told BBC Sport: "In a Celtic team, you are looking for a striker to get you 20 to 30 goals. At the minute, we haven't quite got that.
"I know people are working hard on and off the field to try and get us the goals but replacing someone like Gary Hooper is going to cost you between Â£6million and Â£10million and, at the minute, we are not willing to spend that.
"Looking back at the first AC Milan game; we played really well over there and came away with nothing.
"That's kind of been the story of this campaign. We've not had a great deal of lady luck, we've not really performed to the levels we know we are capable of.
"There are fine lines at this level. The mistakes we've made have been punished and the chances we had, we didn't put away.
"We've been playing well in the league but not shown it in the Champions League. This is cut-throat level football.
"We need to rebuild for next year because the target is to qualify for this competition again.
"We've got a lot of good characters and the manager wants to strengthen again with players that can take us to the next level because we have lost some big players."
Commons admits the heavy defeat in Barcelona, in which Brazil star Neymar scored a hat-trick, left the Celtic players having to "have a long look at ourselves" as they prepare for the visit of Hibernian in the Scottish Premiership on Saturday.
"Once those couple of goals went in before half-time we started to lose our shape and became a little bit disjointed," he said.
"We lost that fight, that desire to stop them putting balls in the back of our net and that's something we haven't struggled with in the last 18 months in this competition.
"Barcelona have outstanding players and it's a very difficult job to stop them.
"We managed it in the last couple of games but we just didn't have that will to win right from the first whistle."