The seven-year-old is hot favourite for the Grade One contest after his defeat of previously unbeaten chaser Sir Des Champs in the John Durkan Memorial Punchestown Chase.
It will be Flemenstar's first attempt at three miles under Rules, but Casey remains confident his stamina will last out.
"Andrew Lynch is very happy with him and I'm delighted," Casey said. "It's all systems go for the Lexus. He's in great form and if we are able to put him to sleep for the first mile that'll be grand.
"He's won over two and a half miles but coming up that hill over the last two furlongs and last two fences will be the test.
"I'm more confident now than I was a few hours ago.
"I wasn't that happy a few hours ago with the rain and everything, but Andrew told me on the phone he's in great form."