No wonder there is anxiety behind the scenes at Celtic.

This is supposed to be a time when all the despair belongs to Rangers, but any time you are near Celtic Park these days you can sense an unease around the place.

On Wednesday night, Celtic face HJK Helsinki in Glasgow in a third qualifying round for the Champions League, and anything other than a successful route to the play-offs for that competition will trigger further tension. In this, of all seasons, Celtic need Champions League football.

You have to whisper this at times, because some Celtic supporters are indignant at the suggestion, but Rangers’ demise is sorely felt by the corporate Celtic.

The very spice of Neil Lennon’s job is in taking on his Old Firm rivals for the SPL title, and Lennon is on record as saying he loves going to Ibrox. But all that is gone for him with Rangers’ exile to the Irn-Bru third division.

Celtic supporters like to crow that, while they are contemplating Europe’s big guns on the field, Rangers’ agenda is now all about Brechin City, East Stirlingshire and trips to Annan.

Well, that’s not how Lennon views it. The Celtic manager, while acknowledging that Rangers deserve their punishment, doesn’t find his job half as exciting without them.

Nor is it just Ibrox crowds that will be very telling in the weeks and months ahead. How will the wider Celtic faithful respond to the possibility of a one-horse title race, let alone, heaven forbid, a season without any Champions League football?

My bet is this: there will be many a Celtic fan who, having revelled in Rangers’ disintegration, suddenly finds the season ahead a lot less enticing.

The afternoon of Saturday July 28 at Parkhead was a case in point. An unimpressive 20,000 turned up to watch what was justifiably billed as a “glamour” pre-season friendly between Celtic and Internazionale. Notwithstanding that we live in an age of austerity, when supporters are counting their money, there was a hint here of apathy surrounding Celtic.

The club itself, as it had to, publicly brushed aside any suggestion of disappointment at this attendance, but it would have been noted with mild apprehension.

Peter Lawwell, the Celtic CEO, will certainly be feeling the heat these days. Lawwell cannot escape the fact that Celtic’s relationship with Rangers, as terse as it can be, is box-office. With the Old Firm now temporarily divorced, the Celtic chief-executive somehow has to find ways of spicing up the menu for his club’s supporters.

How many season-tickets will Celtic sell this season? The club is cagey about that, too. The appetite of 10 years ago, when 54,000 season-tickets would be sold during the Martin O’Neill era, seems long gone.

In recent seasons that figure has dipped sharply, and the worry for Celtic now is that the psychological barrier of 40,000-plus season-books will not be reached. If or when that ever happens, the alarm bells will be jangling.

Lawwell has already betrayed signs of the gathering mood. In sending out his “begging letter” to Celtic supporters recently to snap up season-tickets, he duly hinted at a slower than usual uptake. “We need you back at Celtic Park,” Lawwell told his fan-base bluntly.

In the same letter he aimed a barb at ‘newco’ Rangers when he spoke about Celtic’s “125 unbroken years” of history. In truth, the Celtic chief should probably leave that sort of stuff to the stands and the message-boards.

Celtic should sweep aside HJK Helsinki over 180 minutes. The Glasgow club is 10 times the size of their opponents, with a far superior budget.

Yet all this only increases the pressure on Lennon and Lawwell to hold firm and deliver their club to the Champions League group-stage (and they now enjoy only a narrow 2-1 lead over HJK Helsinki after the home leg: read match report).

The Europa League – the lesser, uglier sibling to the Champions League – is poor consolation.

In terms of crowing and bragging this has been a momentous summer for Celtic supporters. Given Rangers’ severe discomfort, for many of them life could scarcely seem better.

The more discerning Celtic supporter, however, may be wary of the weeks and months ahead.

Follow me on Twitter @GrahamSpiers