Brandon Aiyuk's season went from bad to much, much worse.

Late in the first half, Aiyuk caught a pass over the middle. He was hit and his knee buckled. Aiyuk stayed down on the field. He eventually walked off the field and into the medical tent. At halftime he was carted to the locker room. The 49ers ruled him out shortly after halftime.

Aiyuk held out most of the offseason and preseason with plenty of trade speculation surrounding him, then signed a four-year, $120 million deal to stay with the 49ers. But he had been off to a slow start, with just 351 yards and no touchdowns in six games. Aiyuk dropped a long pass in the first half on Sunday as well.

Aiyuk is the latest big injury for San Francisco. Christian McCaffrey hasn't played all season. First-round pick Ricky Pearsall didn't make his NFL debut until Sunday after being shot in the chest before the season started. Deebo Samuel Sr. played just a few snaps Sunday before leaving the game due to illness.

The 49ers are off to a sluggish start this season, due in part to the injuries. Aiyuk going down won't help.