The San Francisco 49ers' Week 12 game with the Green Bay Packers is close to a must-win for the defending NFC champions, but their star-studded roster appears in poor shape to attack the challenge of coming away from Lambeau Field with a victory.

San Francisco practiced for the second time this week on Thursday, but seemingly did so without quarterback Brock Purdy, defensive end Nick Bosa and left tackle Trent Williams.

If you were listing the players most important to the 49ers' hopes of victory on Sunday, that trio would likely be at the top.

Per Matt Barrows of The Athletic, Purdy was throwing at the very start of the section of practice open to the media but left the field soon after.

There was no Nick Bosa, Trent Williams or Brock Purdy at the start of practice. Purdy, who is dealing with a right shoulder injury, was throwing at the very start of the session but left the field soon thereafter.

— Matt Barrows (@mattbarrows) November 21, 2024

He has been dealing with shoulder soreness sustained in last Sunday's upset loss to the Seattle Seahawks. Purdy did not throw in Wednesday's practice.

Bosa suffered another hip/oblique injury in the defeat to Seattle, doing so on a third-quarter sack of Geno Smith. Williams, meanwhile, battled through an ankle injury in Week 11. Both Bosa and Williams sat out the opening session of the week on Wednesday.

A second straight missed practice does not necessarily mean they will miss the Packers game, with head coach Kyle Shanahan insisting they will be given every chance to prove their fitness to play.

"When it comes to a guy like Bosa, when it comes to a guy like Trent [Williams], their position, the veterans they are, how they play. Those guys have all the way until kickoff for me," said Shanahan. 

"Towards the end of the week I'll have a better feel and he'll have a better feel and that's when we'll discuss."

The likelihood is that the 49ers are being cautious with Purdy ahead of the most important game of the season so far. 

Still, it is far from an ideal turn of events for the Niners and, if they are put in a situation when they are starting Brandon Allen at quarterback without Williams and Bosa, then Shanahan's team may soon find themselves in too deep of a hole from which to climb out and rescue their season.

Could Mother Nature force the 49ers to do something they haven’t done since 2016 against Packers?

It might be on the cards.