GREEN BAY, Wis. — Moments after suffering the franchise’s worst loss to the Green Bay Packers in the history of the series — and the third-largest defeat of any kind since he became head coach in 2017 — the San Francisco 49ers’ Kyle Shanahan was asked to name the most disappointing part of his team’s performance.

Shanahan couldn’t limit himself to just one area and instead spent roughly the next 40 seconds laying out all the ways the Niners failed in Sunday’s 38-10 defeat to the Packers, summing it up best with his opening words.

“The whole game was [disappointing],” Shanahan said. “When you have those penalties, we didn’t stop the run like we did, and we had those three turnovers in the second half. That’s how you get embarrassed.”

Embarrassed was the word of the day in the San Francisco locker room after a beatdown that left them 5-6 and on a two-game losing streak heading into a holiday week with a trip to Buffalo to face the surging Bills next Sunday night.

The loss at Lambeau Field was the franchise’s largest margin of defeat in 74 meetings with the Packers, surpassing a 27-point loss in 1960. The 49ers hadn’t lost to Green Bay by more than 20 since a 21-point defeat in 1997.

What’s more, it was the third-biggest margin of defeat for the Niners since Shanahan took over and their biggest regular-season loss since a 29-point defeat to the Los Angeles Rams in 2018. It also was the team’s worst road loss with Shanahan at the helm.

“This is probably one of the worst ones I’ve been a part of,” 49ers linebacker Fred Warner said. “It is embarrassing. You’ve got to take it on the chin, take it like a man, and move on.”

Moving on this week might be particularly difficult given all of the issues that plagued the Niners. While the team was missing a lot of its star power, including quarterback Brock Purdy (right shoulder), defensive end Nick Bosa (left oblique) and tackle Trent Williams (ankle), the Niners’ frustration was rooted in the many self-inflicted errors they say could have been prevented.

Among the issues Shanahan mentioned: a run defense that was manhandled in the first half (23 Green Bay carries for 125 yards and a touchdown), a pile of missed tackles and costly penalties (a season-high-tying nine for 77 yards), and a trio of turnovers that turned into Green Bay touchdowns.

Included in the penalty parade was a sequence in which the Niners’ defense was flagged on two consecutive plays for having too many men on the field. Shanahan protested the first of those two flags — believing his team hadn’t been given enough time to make a substitution after the Packers made one — but acknowledged the second one was a miscommunication.

“It’s always something, right?” San Francisco safety Ji’Ayir Brown said. “Every mistake we have made — we have been coached, we have been taught, we know exactly what to do. We’ve just got to get it done when it’s time.”

Perhaps none of those miscues was bigger than the pass that went through wide receiver Deebo Samuel’s hands in the third quarter. Down by 10 points on third-and-8 with the ball at Green Bay’s 45-yard line, San Francisco quarterback Brandon Allen fired right for Samuel between a pair of defenders.

The ball slid through Samuel’s hands and into the waiting arms of Green Bay safety Xavier McKinney, who returned it 48 yards to the Niners’ 26-yard line. The Packers scored three plays and a penalty later, and instead of a potential three-point deficit, San Francisco was suddenly down 17.

When it was over, Niners tight end George Kittle pointed to the three things he believed they needed to do to pull off an upset with Allen under center and Bosa and Williams on the sideline.

“Catch everything thrown to us, don’t have penalties and don’t turn the ball over,” Kittle said. “And we didn’t really do all those things, and it kind of just put [Allen] at a disadvantage.”

Making his first start since the 2021 season finale, Allen finished 17-of-29 passing for 199 yards and a touchdown with the one interception. He also rushed twice for 5 yards and lost a fumble on one of the sacks he took.

Kittle said Allen “played his tail off.” And despite Allen’s long layoff between starts, it was clear he wasn’t near the top of the list of problems on Sunday. Still, the Niners are hopeful Purdy will return next week in Buffalo.

“This is probably one of the worst ones I’ve been a part of. It is embarrassing. You’ve got to take it on the chin, take it like a man, and move on.”

49ers LB Fred Warner

Purdy accompanied the team to Green Bay and was seen assisting Allen on the sideline and in the locker room after the game.

After calling the possibility of Purdy playing against Buffalo “up in the air” on Friday, Shanahan said the chances of that happening are still unclear.

“We haven’t done anything since he’s been rehabbing the whole time here,” Shanahan said. “And I’m sure we’ll take him through some stuff early Monday or Tuesday and get a better idea of that.”

Now, San Francisco must turn its attention to another long trip.

Despite their many issues, the Niners are fortunate to be in the messy NFC West, where they sit just a game behind the top teams in the division despite being under .500 at the latest point in a season since 2018.

Following previous losses, the Niners have pointed out that plenty of time has remained to right the ship. But the clock is ticking, and Sunday’s performance did nothing to offer hope that answers are coming soon.

“We all share a bad feeling right now,” San Francisco guard Dominick Puni said. “We’ve got to get back to next week. A big game against the Bills on Sunday night. We’ve got to go.”