(CBS) The Bears spent a large portion of  Thursday’s practice working on special situation football – third downs – as they prepare for Sunday night’s game in San Francisco. Here are other notes from Halas Hall.

Injury updates

Bears starting receivers Brandon Marshall (right ankle) and Alshon Jeffery (hamstring) sat out their second straight practice Thursday as they continue their recovery from injuries suffered last weekend.

Chicago coach Marc Trestman previously said each was “day-to-day,” and he confirmed Thursday that Marshall will attempt to practice Friday. Marshall has maintained that he’ll play Sunday, assuming he has any say.

“I’m going to be out there Sunday, that’s what I’m saying,” Marshall said. ‘But of course, you know, I’m not the head decision maker here. But I’m going to be out there in my mind, and I’m going to be OK.”

Marshall acknowledged there’s risk to aggravate the injury Sunday, but after a loss to the Bills on Sunday, he’s not in the mood to be cautious.

“Well that’s a possibility, but you only get so many opportunities, man,” Marshall said. “There’s a big goal. We dropped one last week, and if I can help the team I’m going to be out there. That’s part of the game, it’s volatile, it’s risky, you know. Hey, I’m going to go down swinging.”

Jeffery’s status seems less certain, though he said earlier in the week the reason he didn’t return against the Bills was for precautionary reasons.

Fellow receiver Josh Morgan (groin) also sat out Thursday’s practice, so the Bears are thin at that position. With that in mind, Chicago signed Chris Williams to its practice squad Thursday, bringing the total receivers to four on that 10-man roster. It’s possible one could get tabbed to play Sunday night if injuries linger for Marshall, Jeffery or Morgan.

Guard Matt Slauson (ankle) and center Roberto Garza (ankle) also missed Thursday’s practice. While the team hasn’t revealed much on their status for Sunday, signs suggest they will miss the game. The Bears re-signed guard/tackle Eben Britton earlier this week for depth, and at Thursday’s media availability, many players spoke as if Brian de la Puente and Michael Ola would be playing.

No change at returner

Trestman confirmed that Senorise Perry will remain the Bears’ primary kick returner, but he added that Santonio Holmes got some work in that role as well. Trestman also confirmed that despite being potentially more involved in the game plan as a wide reciever, Holmes will remain the punt returner.

The Bears now have two return specialists on their practice squad — the newly re-signed Chris Williams and Rashad Ross — so the they’re giving themselves options at kick returner should Perry not distinguish himself or if Holmes assumes a larger role in the offense.

Marshall focused on more yards after the catch

Marshall laments the fumble he lost last Sunday, noting that he needs to secure the ball and also get more yards after the catch.

“Well, for me, man that one hurts,” Marshall said. “I don’t think I’ve fumbled in a year-and-a-half. So, I’ve been really focusing a lot on getting up the field and trying get some more YAC (yards after catch). These last couple of years seem like my production there has dropped, so that’s one of my points of emphasis this year. I’d like to be around 400-500 yards of YAC. So, I’ve just got to do a better job of protecting the ball and protecting it like I have the last few years.”