Brandon Allen didn’t get nearly enough help from his more recognizable San Francisco 49ers teammates as the 32-year-old journeyman quarterback made his first start in nearly three years.

Now, the defending NFC champions find themselves at 5-6 and last in the NFC West.

Allen did a decent job Sunday filling in for the injured Brock Purdy before losing a fumble on a strip-sack by Lukas Van Ness in the fourth quarter of the 49ers’ 38-10 loss to the Green Bay Packers. But on a day when San Francisco’s regulars had to be sharp in Purdy’s absence, the 49ers were sloppy.

Allen threw a 3-yard pass to tight end George Kittle for San Francisco’s lone touchdown.

“I thought he played well,” Kittle said. “We just have to play better.”

That will be necessary if the Niners want to get back to the playoffs. And it would help if they could get healthier.

Right now, San Francisco (5-6) looks like a team missing many of its biggest stars.

Purdy didn’t play Sunday because of a shoulder injury. An ankle injury sidelined three-time All-Pro left tackle Trent Williams. Four-time Pro Bowl edge rusher Nick Bosa was out with a hip/oblique issue. And All-Pro running back Christian McCaffrey still appears slowed by Achilles tendinitis.

Coach Kyle Shanahan didn’t have any immediate update after the game on Purdy’s potential availability for next week, when the Niners visit AFC East-leading Buffalo.

“He’s been rehabbing the whole time here,” Shanahan said. “I’m sure we’ll take him through some stuff early Monday and Tuesday and get a better idea then.”

Allen joined the 49ers last year but hadn’t thrown a pass in a game for them before Sunday. His previous start was for the Cincinnati Bengals in their 2021 finale.

He went 17 of 29 for 199 yards with a touchdown pass and an interception. He fumbled twice, losing one. The interception went through the hands of Deebo Samuel before Green Bay’s Xavier McKinney picked it off.

The 49ers didn’t use the injuries as an excuse.

San Francisco committed three turnovers, had nine penalties and missed 15 tackles in the first half alone. McCaffrey was limited to 31 yards on 11 carries and three catches for 37 yards.

Asked to name the most disappointing part of the game, Shanahan saw no need to limit himself.

“The whole game was,” Shanahan said. “So to label the biggest one — just the first half, the run defense was just real disappointing. I thought we got out of our gaps a number of times. I thought we had way too many missed tackles. Just them being able to control that clock the first half was one of the worst ones I’ve been a part of as far as a half.”

San Francisco struggled to bring down Josh Jacobs, who finished with 106 yards rushing and three touchdowns. He became the first player in the past 55 regular-season games to rush for 100 yards or more against the 49ers. It was the longest a team had gone without allowing a 100-yard rusher since 1955.

Then-Chicago Bears quarterback Justin Fields rushed for 103 yards against the Niners on Oct. 31, 2021.

Jacobs had 91 yards rushing by halftime.

“That’s about as bad as it can get,” Niners linebacker Fred Warner said of the first half. “It was probably the worst I’ve been a part of.”

The Niners trailed 17-7 and got the ball to start the second half. That’s when they had their costliest penalty.

Eric Saubert was flagged for holding to wipe out Samuel’s 87-yard kickoff return that would have given the 49ers first-and-goal. They ended up turning the ball over on downs at Green Bay’s 39-yard line.

The Niners then turned the ball over on three of their next five series, including McKinney’s interception and fumbles from Allen and McCaffrey. Green Bay scored touchdowns after each of those turnovers.