Irish provinces Leinster and Munster have joined the English clubs in making their players unavailable to play for the Barbarians against World Cup winners South Africa.
The Springboks conclude a short tour with a clash against the Baa-Baas on December 1 but the clubs are unwilling to release players due to other commitments.
The decision means Ireland centre Brian O'Driscoll will not captain the invitational side as had been planned.
A joint statement from the provinces read: "Contrary to media reports, neither Brian O'Driscoll nor Paul O'Connell nor any of the selected squads from the Leinster or Munster panels will be available for the upcoming Barbarians match against South Africa."
England Under-18 head coach John Fletcher insists his young side will be better for the experience after beating Italy in the bronze final to round out their 2015 Rugby Europe U18 Championship campaign in style.