Zimbabwe and Bangladesh may be forced to play a shorter programme of Test cricket, if the International Cricket Council's decision-makers agree.
The executive board will meet in October to discuss modifications to the future Test programme.
ICC chief executive Malcolm Speed told a news conference in London: "It may be that there is an option for radical change to the structure.
"We set out to challenge the current thinking and assumptions."
The ICC sought feedback from an exhaustive list of national board chief executives, current captains and former players, sponsors, broadcasters and members of associated members.
The current format has 10 Test nations playing each other home and away over a period of five years.
But that could be altered so that only the top eight nations would continue to play in the same way, with the two lowest-ranked sides - currently Zimbabwe and Bangladesh - involved in a "modified programme."
The matches could stay in a five-year cycle, or be crammed into four years. Most likely, they would be stretched into a six-year timeframe.
A possible opportunity to have four teams playing in a second tier of Test match cricket was eliminated since it was not felt there was enough interest in such a proposal.
The ICC also admitted certain stakeholders had queried the long-time future of Tests over the more commercially viable one-day internationals.
It quoted one broadcaster as saying: "Test cricket is unsustainable and it is only a matter of time before the market kills it."
In a move to reduce the heavy burden on players, the ICC has moved to give them an extra day between back-to-back Tests.
This would mean that rather than two Tests starting on consecutive Thursdays, the second one would begin on a Friday.
The only discrepancy would be the Boxing Day and 2 January Tests traditionally held in Australia, South Africa and New Zealand to maximise holiday time.
There has been no move to impose a maximum number of Tests in a series, with the minimum remaining at two.
Speed said: "In England, Test cricket is very strong. It's not as strong in certain other key markets.
"Some serious marketing effort by some of the other nations will be necessary."
Any changes to one-day international scheduling will only be considered when the modifications to the Test programme are agreed.