For the first time since its inception in 1998, neither Celtic or Rangers have earned a place in the annual Football Money League. In each of the previous Deloitte Football Money League tables, the top 20 has included at least one and sometimes both of the Old Firm.
The 2009 edition is again topped by Real Madrid with income of almost £290 million.
Celtic, who were 17th in last year's list, drop out despite their revenue showing only a minor decrease from £75.2 million in 2007 to £73 million in last year's annual accounts.
Rangers, who were 18th in the list in 2007, recorded record turnover of £64.5 million last season as they reached the Uefa Cup final but remain some distance from the top 20.
Alex Byars, a senior consultant at Deloitte, told The Scotsman: "To be honest, it's quite amazing that one or both of Celtic and Rangers have always featured in the top 20 in the past.
"The reality is that for any club outside the big five European leagues of England, Spain, Italy, France and Germany it is incredibly difficult to achieve the level of revenue required to make it on to the list.
"Fenerbahce have managed it this year, making it in 19th place, and that is largely on the back of reaching the quarter-finals of the Champions League. They are also operating in a larger domestic market than Celtic or Rangers and are doing well commercially.
"Celtic and Rangers both had good years on the pitch last season. Celtic made it to the last 16 of the Champions League for the second year running, while Rangers got to the final of the Uefa Cup, but it is the relatively small broadcasting market they are in which is really holding them back.
"They are also not helped by the depreciation of the Pound against the Euro. We compile the Money League in Euros and the exchange rate for the pound for this year's list was 1.26, while last year it was closer to 1.5. That obviously made a significant difference for all of the British clubs. I think the only way we will see either Celtic or Rangers back in the top 20 any time soon is if they can make major progress in the Champions League. From their point of view, hopefully their performances in Europe this season are just a blip and not a sign of a downward trend."
"In terms of matchday revenue, Celtic and Rangers are still very strong," added Byars. "And while their domestic commercial revenue is some way short of the big five leagues in Europe, it is still fairly healthy compared to others like the Dutch and Portuguese Leagues."
