49ers fearing the worst over Brandon Aiyuk injury following disheartening defeat to the Chiefs

The San Francisco 49ers still can't beat the Kansas City Chiefs, and their latest loss to them was even more painful as it involved a likely season-ending injury to wide receiver Brandon Aiyuk.

Aiyuk was hurt on a third-down reception late in the second quarter of the 49ers' 28-18 defeat to Kansas City at Levi's Stadium.

His knee bent back as he caught the ball between two receivers, with Aiyuk then heading to the locker room at halftime on a cart.

He was quickly ruled out to start the second half and head coach Kyle Shanahan confirmed in his postgame press conference that the Niners are fearing the worst.

"That's what it looks like but we don't know for sure," said Shanahan. "We've been wrong before, so praying that we are."

Aiyuk had already been enduring a frustrating season in the wake of signing a four-year, $120 million extension after a long contract stand-off with the team.

His likely absence for the rest of the year robs the 49ers of their best route-runner, piling pressure on the likes of Deebo Samuel, Jauan Jennings and George Kittle to carry the load.

Samuel barely played against the Chiefs owing to an illness that left him struggling to breathe while Jennings missed out with a hip injury. Jennings is expected to return next week against the Dallas Cowboys.

Kittle, meanwhile, had 92 yards on six catches. The 49ers will need more of that from him, while rookies Ricky Pearsall and Jacob Cowing may be called upon to provide more of an impact after encouraging efforts in defeat.