SANTA CLARA — The strength of the San Francisco 49ers’ offense the past few seasons has been the number of dynamic playmakers that makes it nearly impossible to stop every option.

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A string of injuries has changed that equation and left the 49ers with few proven options for Brock Purdy to throw the ball to in the second half of Sunday’s 28-18 loss to the Kansas City Chiefs.

Star receiver Brandon Aiyuk went down with a serious knee injury late in the first half that was confirmed on Monday to be a torn ACL and MCL that will sideline him for the rest of the season.

Deebo Samuel had already left the game with an illness, No. 3 receiver Jauan Jennings was out Sunday with a hip injury and All-Pro running back Christian McCaffrey has been sidelined all season by Achilles tendinitis that has taken away Purdy’s best checkdown option.

That left Purdy throwing to All-Pro tight end George Kittle and four wide receivers who came into the game with two combined catches this season.

“We had to mix a lot of stuff around there in the second quarter and halftime, or mainly halftime, and those guys were some in spots they didn’t get reps at,” coach Kyle Shanahan said Monday. “For the most part they didn’t make too many mistakes and gave us a chance to get back in the game and gave us a chance to win. Hopefully we can build off of that.”

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Rookies and Veterans Step Up

The 49ers (3-4) will try to get back on track after a shaky start to the season with help from rookies Rickey Pearsall and Jacob Cowing, and little-used veterans Chris Conley and Ronnie Bell.

“Kyle is going to have to scheme some stuff up,” Kittle said. “The nice thing is we still have Jauan Jennings, me, (fullback Kyle Juszczyk), Deebo. We still have guys all over our roster that can make plays.”

San Francisco also could look to make a move before the trade deadline on Nov. 5 to add needed reinforcements to a roster that has been decimated by injuries this season.

“It makes you look into everything,” Shanahan said. “We try to look into everything regardless. Obviously with more issues that came up yesterday, you still want to look into everything, but it has to do with what options are out there with stuff that we can pull off that doesn’t totally hurt us, that helps us now and doesn’t hurt us for the future.”

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What’s Working

Pass defense. San Francisco limited Patrick Mahomes to 154 yards passing with no TDs and also had two interceptions, holding him to a career-low 44.4 rating. The Niners have multiple interceptions in back-to-back games.

What Needs Help

Punt coverage. The Niners allowed another big special teams play when Mecole Hardman returned a punt 55 yards to set up a short touchdown drive. San Francisco had a punt blocked in Week 2, allowed a fake field goal and a long punt return to set up a game-winning kick in Week 3, lost a fumble on a kick return in Week 4 and allowed a kick return for a TD in Week 6.

Stock Up

Pearsall. Just getting back on the field 50 days after being shot in the chest was a big achievement for Pearsall. The first-round pick played 48 snaps and had three catches for 21 yards in his NFL debut.

Stock Down

Purdy. While missing many of his key playmakers, Purdy struggled against the Chiefs defense. He threw three interceptions and posted a career-low 36.7 passer rating.

Injuries

Samuel was hospitalized with pneumonia Sunday night and his status for this week is unknown. … Jennings’ status is also in doubt this week. … Kittle (foot sprain) and Conley (ankle sprain) are day to day … McCaffrey and K Jake Moody (ankle) aren’t expected back until some time after a Week 9 bye.

Key Number

75.1. Shanahan’s offense has struggled against Chiefs defensive coordinator Steve Spagnuolo. In four games against Kansas City with Spagnuolo calling plays, San Francisco has a 75.1 passer rating compared to a 99.7 rating in all other games since 2019.

What’s Next

The 49ers host Dallas on Sunday before getting their bye week.