SANTA CLARA — The San Francisco 49ers got a taste of what their defense looks like without Nick Bosa in the second half of a loss to the Seattle Seahawks.

If Bosa has to miss any more time for San Francisco, it could be crushing to the 49ers’ playoff hopes.

After being held in check for the first two-plus quarters on Sunday, the Seahawks drove for two touchdowns on three possessions after Bosa went out with an injury for a 20-17 comeback win over the Niners.

Bosa expressed concern after the game that he might need to miss some time after injuring his hip and oblique on both sides of the body the past two weeks, but coach Kyle Shanahan left open the possibility on Monday that Bosa wouldn’t have to miss a game.

“We’ll see how it goes this week,” Shanahan said. “Just as good of a chance for him not to play as play. But unless it’s an injury that you know has him knocked out, you always can rule that out early. But when it’s not that case, you don’t decide those things on Mondays.”

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What’s Next

The 49ers visit Green Bay on Sunday.

Deeper Problems for 49ers

The problems for the 49ers (5-5) are deeper than just missing Bosa even if his absence did coincide with Seattle’s success on offense late in the game.

This marked the third time this season that San Francisco blew a fourth-quarter lead to a division rival as the Niners failed to put the game away on offense or defense.

That leaves the 49ers in a three-way tie for second in the NFC West, a game behind leader Arizona. But with three division losses, the Niners have little margin for error to get back to the postseason after making it to the Super Bowl last season and the NFC title game the previous two years.

“That was a tough loss,” Shanahan said. “We had every chance to win it, and we didn’t get it done. So I think guys are disappointed and upset. We all know each other pretty well, and we understand our expectations. We had a good team meeting addressed a bunch of the fourth quarter.”

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What’s Working

Passes to Jauan Jennings. Jennings was the only reliable part of San Francisco’s offense on Sunday. He caught 10 of his 11 targets for 91 yards and a touchdown. Jennings had seven first downs on his 10 catches, including four that converted third downs. Brock Purdy had a 131.4 passer rating when throwing to Jennings and a 48.2 rating on all other throws.

What Needs Help

Closing out games. The Niners have blown fourth-quarter leads in division losses to the Rams, Cardinals and Seahawks. In all of those games, the offense had the ball with a chance to put the game away. But San Francisco failed to score on drives in all three games when leading by a score, setting the stage for the opponent to rally for the win.

The Niners got the ball back with a four-point lead and 3:56 to play on Sunday. After getting two quick first downs, the offense stalled with Christian McCaffrey losing 1 yard on a first down run, Purdy missing Deebo Samuel on a second down pass and then Jennings getting stopped for a 5-yard catch on third-and-11.

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Stock Up

RG Dominick Puni. The rookie had another strong game as he allowed only one pressure and was the only Niners starting lineman who didn’t commit a penalty. Puni has allowed no sacks and no QB hits all season, according to Pro Football Focus. Puni and Kansas City’s Joe Thuney are the only guards with at least 500 snaps who haven’t allowed a sack or a QB hit.

Stock Down

With Brandon Aiyuk out for the season with a knee injury, the Niners have needed more production from Samuel. That hasn’t happened. Samuel had four catches on seven targets for 22 yards and ran the ball once for a loss of 1 yard. After topping 100 yards from scrimmage nine times in 19 regular season and playoff games in 2021, Samuel has done it just eight times in his past 43 games.

Injuries

Purdy has a sore right shoulder from a hit on Sunday and is day to day. … TE George Kittle is expected to be back at practice Wednesday after missing the game with a hamstring injury. … CB Charvarius Ward has rejoined the team after missing the past two games following the death of his 1-year-old daughter. … WR Jacob Cowing is concussion protocol. … LB Tatum Bethune injured the MCL in his knee and will be out for a while.

Key Number

5. The 49ers became the fifth team since the merger to lose three division games in a season that they led in the final two minutes of regulation, according to the Elias Sports Bureau. The other teams to do it were Carolina in 2001, San Diego in 2000, Baltimore in 1996 and Washington in 1994.