The 49ers fear WR Brandon Aiyuk tore his right ACL in the loss to the Chiefs

SANTA CLARA, Calif. – On a day when the San Francisco 49ers celebrated the return of one wide receiver, they lost another – possibly for the season.

Brandon Aiyuk, who led the Niners in receiving categories the past two seasons, suffered what the team fears was a torn anterior cruciate ligament in his right knee during Sunday's 28-18 loss to the Kansas City Chiefs.

If the further tests Aiyuk will undergo in the next 24 hours confirm this diagnosis, Aiyuk will require surgery and will miss the rest of the season.

“It looks like that, but we don’t know for sure,” coach Kyle Shanahan said. “I've been wrong before. So I pray we do.”

Entering the day, Aiyuk was the only healthy 49er among the team's top three wideouts. Jauan Jennings was ruled out Friday with a hip injury, while Deebo Samuel came to Levi's Stadium due to illness, which was announced about 30 minutes before the game with the caveat that Samuel was expected to play.

Samuel entered the field shortly before the start of the game and took part in the coin toss, but moved slowly. He played four snaps but quickly retreated to the sideline and did not return. Before his day was over, he had no catches or carries.

“Throat, stomach, just really tired,” Shanahan said. “He was having a hard time breathing, he couldn't catch his breath…he kept trying to fight through it, but when he had trouble breathing and everything, we had to shut him down.”

While the Niners hope Jennings and Samuel will be back for next week's game against the Dallas Cowboys, Aiyuk's situation appears to be more serious.

With 48 seconds left in the second quarter, Niners quarterback Brock Purdy found Aiyuk between two Kansas City 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.

At the time of his departure, he had two catches for 23 yards, leaving receiver duties to veterans Chris Conley and Ronnie Bell and rookies Ricky Pearsall and Jacob Cowing.

“It sucks,” tight end George Kittle said. “I love Brandon Aiyuk, the energy he brings, what he can do on the football field, his ways of catching the ball. He's an incredible football player…In my opinion, you can't really replace one of the best receivers in the NFL.”

The 49ers signed Aiyuk to a four-year, $120 million contract extension in August after a lengthy contract dispute nearly resulted in him being traded to several teams, including the Pittsburgh Steelers and Cleveland Browns.

In 2023, Aiyuk had 75 receptions for 1,342 yards and seven touchdowns en route to second-team All-Pro honors. However, he got off to a slower start this year with 25 catches for 374 yards and no scores.

Still, the loss of Aiyuk is no small thing, especially when compared to the other serious injuries that continue to mount for the Niners. If Aiyuk were to be out for an extended period of time, he would be among the most important 49ers, along with running back Christian McCaffrey (Achilles tendonitis), linebacker Dre Greenlaw (torn Achilles tendon), defensive tackle Javon Hargrave (torn triceps) and safety Talanoa Hufanga (torn wrist ligaments).

That would also put additional pressure on Pearsall, the No. 31 pick in April's draft, to produce faster than expected. Pearsall made his debut on Sunday, just 50 days after he suffered a gunshot wound to the right side of his chest during an attempted arm robbery in San Francisco.

“What BA does for our offense and who he is and as a teammate and brother of ours, man, it’s sad,” Purdy said. “I wish him nothing but the best and am praying for him. So that's my type. And when he goes down like that, of course we have other people who can step up and do their jobs really well…we just have to all come together as a group, the receiving unit and all of us.”