Westerman is nursing an ankle injury.
Warrington coach Tony Smith said the back-rower is his only injury concern for Wembley.
“Everyone else is fit as a fiddle and ready to go,” Smith said.
Hull FC have no injury problems heading into the final.
“We’re all good to go,” Hull coach Lee Radford said.
Smith said with hot weather expected for Saturday it could bring an openess to the game.