The BBC Trust has withheld approval of plans for a new Gaelic Digital Service (GDS) until more evidence of its wider appeal has been demonstrated.
The service would involve television, radio and online
The trust also said further evidence of educational benefits must be shown.
The service has been planned in partnership between BBC Scotland and the Gaelic Media Service (GMS).
Giving its provisional conclusions, the trust said the new channel could deliver public value but that more information was required.
The television, radio and online service would cost £24.8m annually assuming it launched on Freeview in 2010 and would involve funding from the BBC and GMS.
The figure breaks down into £10.1m from GMS and £14.7m from the BBC.
In turn, the BBC funding includes £7.2m it already spends on Gaelic content with the other £7.5m comprising £2.5m new spending on content and £5m on distribution.
The GDS television service would be on air for about seven hours per day.
This will include about 1.5 hours of new content.
The trust, which monitors how the corporation spends the licence fee, said it believed the service could deliver substantial public value and that there was a great deal of support for the channel from the public.
However, National Trustee for Scotland Jeremy Peat said the proposal was lacking details.
The BBC and GMS partnership now has until 19 December, when public consultation ends, to provide more evidence on the educational and wider audience benefits.
A final decision will be taken in January, although the government-funded GMS has already promised to press on with plans for the new channel with or without the BBC.
Earlier this month, a public value assessment concluded that the service must offer more to justify the level of spending needed.
Tory culture spokesman Ted Brocklebank said his party was committed to the principle of a dedicated Gaelic digital service.
He added: "But I agree with the BBC Trust's findings that the new GDS needs to produce more Gaelic speakers rather than simply enhancing the service."
Angus MacNeil, SNP MP for the Western Isles, described the trust's position as offering a challenge to the Gaidhealtachd.
He said: "The Faroe Islands has a community of 48,000, yet supports two dedicated television services, together with three radio stations.
"I have consistently asked the government to commit to a transmission date for the new Gaelic service, and have been met with a series of evasions and weasel words designed to leave the BBC lots of wriggle room."
He added: "I hope that there is no-one out there who feels they may have been overlooked as the BBC Trust reaches this provisional conclusion."