Taulupe Faletau joining Bath would undermine Gatland's Law, according to ex-Wales fly-half Jonathan Davies.
Dragons' Wales forward Faletau, 24, has been linked with the English side.
Under the so-called 'Gatland's Law', Wales-based players are likely to be favoured for Test selection over those who choose to play elsewhere.
"If a player on the fringes left, then the law is easier going. Players of Faletau's calibre leaving is a different story," Davies said.
In August, 2014, the Welsh Rugby Union and Wales' four professional regions signed a £60m, six-year deal that settled a long-running dispute over the sport's future.
That deal included rules that mean players based outside Wales could be overlooked in favour of home-based talent, with coach Warren Gatland expected to tighten selection policy.
The policy ruled that no player based overseas should represent Wales, although Gatland is able to make exceptions.
Tonga-born Faletau had his offer of a national dual contract withdrawn by the Welsh Rugby Union in May.
He said at the time that changing his agent had "delayed" signing a dual contract, which would be co-funded by the WRU and the region.
Faletau has a year left on his Dragons contract but could be bought out of that deal, with speculation the region could ask for as much as £250,000.
It is possible Faletau, capped 45 times by Wales, will join Bath after this autumn's World Cup, while Cardiff Blues are awaiting a reply from the player's agent after making their offer.
Former Bath and England centre Jeremy Guscott believes Faletau's trophy ambitions may be better served playing outside Wales, a view which Davies shares.
"If he's going to go and get silverware then he'll have to leave Newport Gwent Dragons and maybe Wales," Davies added.
"If you look at the players who have left Wales, most of them go for the salary and also an opportunity to win things," Davies added.
"If you look at it from Taulupe's point of view, imagine what he would be like playing behind a very, very strong side.
"The opportunity for him would be immense."