The Hoops were ruthlessly punished for a below-par display in the Nou Camp as they crashed to a 6-1 defeat, only the second time in 10 matches against Barcelona that the outcome has been decided by more than one goal in favour of either team.
There has been much negativity aimed at the Scottish champions in the aftermath of the loss, but Lennon insists Celtic are living within their means and working within constraints and that spending big money does not assure success.
Celtic were unable to match their impressive feat in the Champions League last season when they reached the last 16, as they lost out to Barca, AC Milan and Ajax to finish bottom of their group this time around.
Lennon said: "We are in a difficult position because of where we play our football domestically.
"Then you've three qualifiers. Then you've no guarantee that you'll get to the Champions League. Eventually when you do you've got a two-week window to try and attract players to come and play and that's a difficult thing to do.
"Now even if we had spent £7m on a striker, would that have guaranteed us getting into the last 16? It may have made us a little bit better but maybe weaker in other areas of the pitch.
"Shakhtar Donetsk have spent £160m, didn't qualify. Juventus didn't. Napoli, who were very unfortunate not to, they haven't. And nor have Benfica.
"I think we overachieved last year. We finished fourth in a group where we were seeded fourth this year. And it is what it is.
"Now we will always look to invest in the team when we can. And we'll look to do that in January. But it can't always be the perfect scenario that we all want."