Welsh Rugby Union group chief executive David Moffett says that plans for a new five-nation provincial tournament are far from complete.
Wales, Scotland and Ireland are in talks with Italy and South Africa for a new 24-team Rainbow Cup competiton for their provincial sides.
It could start this September, but Moffett says it is not a done deal.
"We're waiting on contracts, sponsors and restructuring in Italian and South African rugby," Moffett told BBC Sport.
"The promoters from South Africa have gone away to work on the fine detail.
"There are quite a few issues to be resolved, but the next 10 days or so will tell us.
"Things have been rushed through in the past, and if this concept is to get off the ground it needs to be done properly.
"We are in favour of stability. If changes are to be made they will be for a significant period of time with long-term contracts in place."
Despite his reluctance to commit to any definite plans, Moffett insisted that the proposed tournament could bring real value to Welsh - and Celtic - rugby.
"The proposal to involve the top South African provinces could have a very positive effect on Welsh rugby," he said.
"We've always said that if we want to be the best we have to play the best and they have some fantastic teams.
"And talks to give Italian teams more involvement in a competitive league actually originated from the WRU following Wales' Six Nations game in Rome this year."
Should the Rainbow Cup go ahead, Moffett suggested that it would mean the Celtic League reverting to a home or away basis with four Italian sides brought into a 15-team tournament.
He also insisted that it would not necessarily rule out the future introduction of an Anglo-Welsh Cup.
Such a tournament came close to being organised for next season before being scuppered by fixture congestion and the opposition of the Irish and Scottish unions.