49ers-Seahawks pregame: Geno Smith is out; Niners do Knapp Stair Climb Challenge

SANTA CLARA — Geno Smith was inactive Sunday for the Seattle Seahawks, with the 49ers instead tasked with defending backup Drew Lock at Levi’s Stadium.

Smith gingerly went through a 10-minute workout some three hours before kickoff to determine and it was clear by warmups he would sit out the game with a groin injury as he watched Lock and Sean Mannion go through drills.

Mannion was added to the 53-man roster as an option after Smith sustained a groin injury in Thursday’s practice, which caused him to be listed as questionable.