But Leinster coach Joe Schmidt remains hopeful his star centre will pass a late fitness test before travelling with the squad to Cardiff.
"There's still some residual swelling on his knee but hopefully he will be OK. We're travelling late tomorrow late afternoon and Brian will have a run around before we leave," said Schmidt.
Prop Richardt Strauss, one of five players injured in what Schmidt described as a "demolition derby" against Ulster, has also overcome a bruised hip and will be available for the eagerly-awaited showdown between the rival front-rows.
Meanwhile captain Leo Cullen revealed he is more nervous for this game than either of his previous two appearances in finals, with Leicester in 2007 and Leinster in 2009.
"I've been wound up about this game all week," said 33-year-old Cullen.
"I might be a bit older and more experienced, but I'm certainly not more chilled out.
"It's my third final and I've won one and lost one so I've experienced both emotions. But even with that behind me, I still haven't learned to cope with the stress."