England hooker Mark Regan looks set to be denied the chance to captain the Barbarians against South Africa on Saturday.
Bristol, the front-row's club, were happy to rest Regan from this weekend's Anglo-Welsh Cup game with Leeds where, regardless of the result, they cannot reach the last four.
But the 35-year-old has not been given permission to face the world champion Springboks because this would be in breach of contract.
Premier Rugby, which runs the 12-team Premiership, can bar players from appearing for the invitational Barbarians side because this fixture does not take place on an agreed international weekend.
Regan's Test front-row colleague Andrew Sheridan, who plays for Sale, is likely to be barred from this weekend's Twickenham match for the same reason.
The umbrella body only recently signed an agreement with England's Rugby Football Union regarding the vexed issue of player release for full Tests following a series of "club versus country" rows.
Premier Rugby are determined that players at member sides will not turn out for other teams any more than they have to under existing agreements and international rules.
Bristol chief executive David White told BBC Sport: "Premier Rugby have made their decision and we are supporting that. We have not released him, he can't play and we have the jurisdiction to fine him. If he does play he'll be breaking his contract and will have to face the consequences."
South Africa, who last month beat an England side featuring Regan and Sheridan 15-6 in Paris to win the World Cup final, defeated Wales 34-12 last Saturday at the Millennium Stadium in their first Test as world champions.
Both Springbok coach Jake White and Eddie O'Sullivan, the Ireland coach who has been put in control of the Barbarians for this fixture, were expected to name their starting sides yesterday.