Brandon Aiyuk (knee) and Deebo Samuel (illness) of the 49ers are out against the Chiefs

SANTA CLARA, Calif. (AP) — The San Francisco 49ers have already lost one of their top three receivers, losing wideouts Deebo Samuel and Brandon Aiyuk to illness and a right knee injury, respectively, against the Kansas City Chiefs on Sunday.

The biggest concern was Aiyuk's injury. With 48 seconds left in the second quarter, Niners quarterback Brock Purdy found Aiyuk between two Chiefs defenders for a 15-yard gain. Chiefs defenders Chamarri Conner and Trent McDuffie were closing in on Aiyuk when he took a low hit, leaving his knee in a precarious position.

Aiyuk remained down as the Niners' medical staff came to help before he was able to stand, slowly hobble to the sideline and walk to the medical tent. He went to the locker room shortly afterward and a return was ruled out early in the third quarter.

Aiyuk's injury came after Samuel fell ill with an illness on Sunday morning. Samuel didn't do much during warmups and the team announced he was sick but expected to play.

Samuel entered the field shortly before the start of the game and took part in the coin toss, but moved slowly. Before his day was over, he had nothing to catch or carry.

On Sunday, San Francisco was already missing Jauan Jennings, who suffered a hip injury in last week's win against the Seattle Seahawks.

Without their top three receivers, the 49ers will be without veterans Chris Conley and Ronnie Bell as well as two rookies, Ricky Pearsall and Jacob Cowing.

Pearsall, the No. 31 pick in April's NFL draft, is playing in his first regular-season game 50 days after he was shot in the chest in a suspected robbery attempt.