Seattle placed Penny (ankle/fibula) on injured reserve Friday, John Boyle of the Seahawks' official site reports.
Penny's move to IR was merely a formality after he underwent season-ending surgery Tuesday to repair his left ankle and fractured fibula. The transaction opens up a spot on the 53-man roster, but it's unclear if Seattle plans to use it on another running back. Seattle already claimed Tony Jones off waivers from New Orleans earlier this week to add depth behind rookie Kenneth Walker, who is expected to step into a lead role out of the backfield beginning with Sunday's game against the Cardinals.