49ers' Brandon Aiyuk (knee), Deebo Samuel (illness) exit vs. Chiefs - ESPN

SANTA CLARA, Calif. — Already missing one of their top three receivers, the San Francisco 49ers lost wideouts Deebo Samuel and Brandon Aiyuk to an illness and a right knee injury, respectively, on Sunday against the Kansas City Chiefs.

Of more pressing immediate concern was the knee injury to Aiyuk. With 48 seconds left in the second quarter, Niners quarterback Brock Purdy found Aiyuk between two Chiefs defenders for a gain of 15 yards. Chiefs defensive backs Chamarri Conner and Trent McDuffie converged on Aiyuk as he took a low hit, leaving his knee in a precarious position.

Aiyuk stayed down as Niners medical personnel came out to help before he was able to get up, slowly limp to the sideline and head to the medical tent. He went to the locker room soon after and a return was ruled out as the third quarter opened.

The injury to Aiyuk comes after Samuel came down with an illness Sunday morning. Samuel didn't do much in warmups and the team announced that he was sick but expected to play.

Samuel walked onto the field just before the game started and participated in the coin toss but was moving slowly. He did not have a catch or carry before his day came to an end.

Entering Sunday's game, 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 are down to veterans Chris Conley and Ronnie Bell and a pair of rookies, Ricky Pearsall and Jacob Cowing, at receiver.

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