INGLEWOOD, Calif. – San Francisco 49ers tight end George Kittle will miss Sunday's game against the Los Angeles Rams because of a hamstring injury.

The Niners removed any doubts about Kittle's status on Saturday when they officially declared him out. With Kittle unavailable, the 49ers activated tight end Brayden Willis from the practice squad to provide additional depth behind tight ends Eric Saubert and Jake Tonges.

Star defensive end Nick Bosa, who was listed as questionable because of a rib injury, will be active against the Rams. Bosa participated in full practice on Wednesday but was limited for the next two days after injuring his rib during a one-on-one drill on Thursday.

Defensive end Sam Okuayinonu was also promoted from the practice squad to the active roster, providing additional depth.

Niners coach Kyle Shanahan said Friday that Kittle was sore after fully participating in practice on Wednesday and reported similar pain on Thursday. Kittle did not practice on Friday because the pain persisted, which led to his participation being initially listed as questionable.

San Francisco will be without Kittle, running back Christian McCaffrey and wide receiver Deebo Samuel for the game against the Rams. McCaffrey is on the injured list with Achilles tendinitis and Samuel is expected to be out for a few weeks with a calf injury.

Saubert is expected to start in Kittle’s place.

“I thought he did a heck of a job,” Shanahan said of Saubert on Friday. “He contributed well. Kittle was cramping most of the game, so he had to do a lot during the Minnesota game. He's been really consistent since he's been here. If he has to do everything, he's up to the challenge. He showed he can help us in the passing and running game.”