SANTA CLARA, Calif. – Less than 24 hours after wide receiver Brandon Aiyuk injured his right knee against the Kansas City Chiefs, the San Francisco 49ers received the expected bad news.

Aiyuk has torn the anterior cruciate ligament and medial collateral ligaments in his right knee, which will require surgery and will end his 2024 season after just seven games, coach Kyle Shanahan announced Monday.

Additionally, the illness that limited receiver Deebo Samuel to four snaps against the Chiefs is technically a form of pneumonia, according to Shanahan. Samuel has fluid buildup in his lungs and remains at a local hospital after being checked in Sunday evening.

“I think it started moving in the middle of the night Saturday night or early Sunday morning and then it kind of progressed throughout the day,” Shanahan said. “When we found out after the game that he had the fluid in his lungs and stuff, I think they sent him there.”

Shanahan said there is no timetable yet for when Samuel might return, but that should become clear in the next few days.

Aiyuk, on the other hand, is not expected back at all this season. Further testing Monday confirmed what Shanahan expected Sunday night. After a 28-18 loss to the Chiefs, Shanahan said that all signs pointed to a torn ACL but that it still needed a closer look and that the Niners were “praying” they were wrong. They weren't.

Aiyuk's injury occurred with 48 seconds left in the second quarter. Quarterback Brock Purdy squeezed a pass to Aiyuk between Kansas City defenders Chamarri Conner and Trent McDuffie for a 15-yard gain. As Conner and McDuffie approached Aiyuk, his knee appeared to hyperextend.

The Niners' medical staff immediately rushed onto the field to tend to Aiyuk, who remained down for several minutes before slowly limping toward the sideline and toward the blue medical tent. Soon he was taken to the locker room on a cart.

Aiyuk had two catches for 23 yards at the time of the injury, marking a relatively slow start to the season. With his season over, Aiyuk will be unable to reach 1,000 receiving yards for the third straight year. He had 75 receptions for 1,342 yards and seven touchdowns en route to his All-Pro second-team nomination last year.

“I talked to him last night and I just called him at his house,” Shanahan said. “He was hurting, he was just as beside himself as you would expect. But he's a strong and spiritual guy and believes everything happens for a reason, so he'll be fine. But last night I was definitely a little depressed and I was just telling him how sorry I am and letting him know that we are all here for him in this situation.

The Niners signed Aiyuk to a four-year, $120 million contract extension in August after a lengthy contract dispute. He finished this season with 25 catches for 374 yards and no scores.

Aiyuk's torn ACL is the latest in a growing list of injuries to key 49ers. Running back Christian McCaffrey (Achilles tendonitis), linebacker Dre Greenlaw (torn Achilles tendon), defensive tackle Javon Hargrave (torn triceps) and safety Talanoa Hufanga (torn wrist ligament) are among the other key Niners missing significant time.

“It sucks,” center Jake Brendel said Sunday. “Any injury like that to any of your weapons on offense or defense just sucks. I have the feeling as a squad that we simply have to react. Whoever is next on the roster needs to step up and make sure there is no setback and productivity on offense.

With Aiyuk lost this season, the 49ers hope to get Samuel and Jauan Jennings back for Sunday night's game against the Dallas Cowboys. Jennings did not play against Kansas City due to a hip injury suffered in a win against the Seattle Seahawks on October 10.

If they don't get one or both of Samuel and Jennings for the game in Dallas, the Niners would have to again turn to a group that includes rookies Ricky Pearsall and Jacob Cowing, second-year wideout Ronnie Bell and veteran Chris Conley even in everyday life with an ankle injury.

“He was hurting, he was just as beside himself as you would expect. But he's a strong and spiritual guy and believes everything happens for a reason, so he'll be fine. But last night I was definitely a little depressed and I was just telling him how sorry I am and letting him know that we are all here for him in this situation.

49ers coach Kyle Shanahan on his conversation with WR Brandon Aiyuk

“With Jauan and Deebo, I’m not sure if we’ll get them back this week or not,” Shanahan said. “So, it was a good start for these guys and they should have a lot more to come.”

Tight end George Kittle, who picked up most of the pass-catching break against the Chiefs with six catches for 92 yards, is also dealing with a day-to-day ankle sprain.

Shanahan said the Niners also don't expect to get McCaffrey, Greenlaw or kicker Jake Moody back this week.

“Christian is still making progress in his rehab,” Shanahan said. “He hasn’t suffered any setbacks, so it’s good news so far. I would be surprised if I got him back this week, but I hope the bye week goes well and I have a much better chance there straight after the bye week.” .”

Shanahan hinted that Moody could return even after the Week 9 bye, but Greenlaw will likely take a little longer.