Taulupe Faletau's proposed move to Bath is in doubt after Wales head coach Warren Gatland suggested he would not sanction the deal.
The Wales and Newport Gwent Dragons number eight, 24, has long been linked with a move to the Rec.
But under the terms of the Rugby Services Agreement between the Welsh Rugby Union and the regions, Gatland would need to approve such a transfer.
"I would be limiting myself and why would I do that?" said Gatland.
"At the moment, unless something changes, hopefully he will be playing in Wales."
Faletau had seemed set to join Bath, with Dragons believed to be considering selling the British and Irish Lions forward for a six-figure fee.
Because Faletau has a year left on his current Dragons contract and is a Wales player, the Rugby Services Agreement stipulates that Gatland would need to approve such a transfer to an English club.
In May the WRU withdrew its offer of a national dual contract to Faletau after he missed a deadline.
Two wildcard selections
Under the so-called 'Gatland's Law' selection policy, Wales-based players are likely to be favoured for Test selection over those who choose to play elsewhere.
If Faletau was to join Bath, his chances of playing for Wales could be restricted because Gatland only has two selection wildcards for players in the same circumstances.
Centre Jamie Roberts and fly-half Rhys Priestland, who have joined Harlequins and Bath respectively, are two such players.
"Given that Wales has such a small playing base, I have dispensation to pick a certain number of players playing outside Wales. This year that is two," Gatland told Sky Sports News.
"At the moment, if Taulupe Faletau goes to Bath there would be three players and I could only pick two after the World Cup.
"Jake Ball had a huge offer from Northampton, but he decided to stay in Wales because he wanted to play for Wales.
"If we lose three or four players in a position, I can go to the regions and request that we can select a player from England or France."