Sale have demanded Sheridan play in Friday's Anglo-Welsh Cup clash with Leicester and the Barbarians have fallen into line, even though they claim contractually he is obliged to play for them.
A replacement for the destructive Lions front row will be announced when coach Eddie O'Sullivan names his team to face the world champions.
"We've had problems with Sale over Andrew," said a Barbarians spokesman.
"We respect Sale's point of view and are not pursuing the finer detail of the contract we have with Andrew.
"We have accepted Andrew will not play for the Barbarians on Saturday."
The stand-off over Regan continues, however, with the combative England hooker determined to skipper the invitational side.
Bristol have warned Regan he will be in breach of contract if plays in the match but the Barbarians maintain he will appear at Twickenham.
"Mark is playing and there's nothing left to say on the matter," added the spokesman.
"He's accepted the invitation to captain the Barbarians and he will lead the team onto the field.
"We can confirm he joined up with the team for training yesterday. He's made the decision that he wants to play and is sticking to it."