The San Francisco 49ers will be without their top two players on offense and defense when they play Sunday’s critical game against the Green Bay Packers.

Quarterback Brock Purdy and wide receiver Nick Bosa have each been ruled out for the game, coach Kyle Shanahan said Friday. Additionally, the 49ers could also be without left tackle Trent Williams.

The soreness in Purdy’s right (throwing) shoulder was bad enough that he will miss the first game of his three-year career. Linebacker Brandon Allen will start against the Packers. Shanahan said he doesn’t think Purdy’s injury will be a long-term problem. But the severity of the pain caught the 49ers by surprise.

Purdy was a limited participant in Wednesday’s practice and threw lightly before Thursday’s practice, but left the session early and raised concerns.

“I don’t want to say there’s a long-term concern, you know we had the MRI on Monday, we thought he just needed rest and we weren’t worried about him not being good this week,” Shanahan told reporters on Friday . . “But when it started on Thursday, it just surprised him, it surprised us how we felt. So we had to shut it down and I really don’t know what to think about it. The MRI doesn’t look like it, so it should be fine, but the way he responded this week, it’s really up in the air for next week. So we’ll have to see on Monday.”

There was concern about Bosa after he left the game with right side soreness in the third quarter and did not return during the 49ers’ Week 12 loss to the Seattle Seahawks last week. Bosa has been ruled out with both hip and oblique injuries.

Williams will be a game-time decision after testing his ankle in pregame warmups. The team is optimistic that they will play, even though they haven’t practiced all week.