The half-backs, who guided Wales to their first Slam in 27 years, had been invited to play for the Barbarians this summer – including a match up with their country on June 2.
But the former Scarlet stars have been forced to pull out of potentially their last appearance at the home of Welsh rugby due to injuries.
Welsh record try-scorer Shane Williams and Ospreys team-mate Duncan Jones remain in the Baa-Baas squad to face Rob Howley’s men.
Williams retired from international rugby against Australia in December and will quit the professional game altogether following the showdown, while Jones’ last appearance at the Millennium Stadium was in 2009.
The star-studded Baa-Baas still boast the likes of Mils Muliaina , Cedric Heymans, Mike Tindall and Stephen Donald.
They have also called up former Cardiff Blues centre Casey Laulala, Australian Mark Chisholm and Italy’s Cornelius van Zyl.
