LUCKLESS Hawthorn utility Brendan Whitecross has been ruled out of next week's Grand Final and could face another lengthy stint on the sidelines amid fears he has again ruptured his right anterior cruciate ligament.

Whitecross came on as the Hawks' substitute midway through the third term of their thrilling five-point preliminary final win over Geelong on Friday night.

The 23-year-old re-injured his knee when he lunged sideways in an attempt to tackle Geelong defender Cameron Guthrie in the final quarter.

Hawks coach Alastair Clarkson said after Friday night's game the extent of Whitecross' injury would not be known until he had scans.

"We'll get that confirmed probably tomorrow or Sunday. Whatever it is, it's a serious enough injury for him to miss next week, so that's heartbreaking for ‘Whitey’ and his teammates and our club," Clarkson said.

"But we'll wait and see what transpires over the next couple of days."

Whitecross missed the Hawks' Grand Final clash with the Sydney Swans last year after rupturing his right ACL early in their qualifying final win over Collingwood.

He made a speedy recovery to return in round 14 this year and had played every game since then.

Clarkson said he planned to speak to Hawthorn fitness staff on Friday night to work out whether they would rest Whitecross' possible Grand Final replacements from Sunday's VFL decider.

Hawthorn's VFL affiliate Box Hill plays Geelong for the VFL premiership, but the Hawks might be reluctant to play preliminary final emergencies, Jed Anderson and Kyle Cheney, and fringe player Taylor Duryea given they would only have a six-day break before next Saturday's Grand Final.