Penrith will be without star winger Brian To'o for Saturday's semi-final clash against western rivals Parramatta.

The Panthers confirmed on Friday night that the New South Wales flyer has been sidelined with an ankle injury and will not feature for Ivan Cleary's side at BB Print Stadium.

To'o's absence is a major blow for the Panthers, who will be looking to keep their season alive after falling to South Sydney in last week's qualifying final.

The loss means Penrith will now take the long route in their hopes of securing their first premiership since 2003, with a win against the Eels setting up a preliminary final clash with minor premiers Melbourne.

To'o has enjoyed a career-best campaign in 2021, scoring 14 tries and averaging 247 running metres from his 19 appearances this year.

Penrith Panthers Training Session
SYDNEY, AUSTRALIA - OCTOBER 20: Brent Naden of the Panthers runs the ball during a Penrith Panthers NRL training session at Panthers Stadium on October 20, 2020 in Sydney, Australia. (Photo by Mark Kolbe/Getty Images)

The 23-year-old will be replaced by centre Brent Naden, while Tyrone May was the other omission from Cleary's 21-man squad.

Final 18-man squads will be released at 6:50pm AEST.