The midfielder was speaking after the 6-1 defeat by Barcelona at Camp Nou on Wednesday left the Scottish champions bottom of Group H with three points and without the prospect of European football in the New Year.
After Hooper, Celtic's leading scorer, moved to Norwich City in the summer, the club 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 dropped to the bench against Barcelona where Georgios Samaras' late consolation goal was only Celtic's third in six group games. The former Nottingham Forest and Derby County player believes the Parkhead club needed to bite the financial bullet to replace Hooper.
"In a Celtic team you are looking for a striker to get you 20-30 goals," said Commons. "At the minute, we haven't quite got that. I know people are working hard on and off the field to try to get us the goals but replacing someone like Gary Hooper is going to cost you between £6m and £10m and 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. 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."
Commons admits the heavy defeat in Camp Nou, in which the Brazilian Neymar scored a hat trick, left the Celtic players to "have a long look at ourselves" as they prepare for the visit of Hibernian in the spfl Premiership tomorrow.
"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."