Jonathan Sexton is out of Leinster's Heineken Cup semi-final with Toulouse tomorrow (Sat).
The Ireland fly-half has failed to recover from the fractured jaw he sustained in the quarter-final win over Clermont Auvergne three weeks ago.
And Leinster coach Michael Cheika confirmed that Shaun Berne will deputise at outside half in the south of France.
Cheika said: "Jonny was desperate to play and we gave him every opportunity. But we felt it was too big a risk and we also have the player's welfare and safety in mind.
"But we have 100 per cent confidence that Shaun Berne can do the job."
Isa Nacewa is expected to be the Irish province's back-up as number ten and as a goalkicker with centre Fergus McFadden remaining doubtful with a calf injury.
