Jimmy Garoppolo is seeking additional medical opinions to determine whether he will require season-ending surgery on a high ankle sprain.
Meanwhile, All-Pro tight end George Kittle is expected to miss eight weeks due to a fractured foot. His injury likely brings an end to his season.
Both players will go on injured reserve after sustaining injuries Sunday against the Seattle Seahawks, 49ers coach Kyle Shanahan said on Tuesday.
Garoppolo could be out of action six weeks, but he would end up being sidelined for the remainder of the season if he opts for surgery.
Garoppolo missed two games earlier this season with a high ankle sprain on his left ankle, too.
"He essentially had a whole new one, just on the same foot," Shanahan said. "When you have those high ankle sprains, you re-injure them a lot. But it was a different way he did it. So it’s basically doing it all over again in a different way.
"It is worse than the last one. That’s why surgery is an option. We’re getting different doctors’ opinions now. Whatever is best for him long term is obviously what we’ll decide on. But if he does need the surgery, it’ll be all year. Hoping six weeks to get him back at the end."
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Kittle underwent X-rays at the stadium in Seattle shortly after he was removed in the fourth quarter from the 49ers' 37-27 loss on Sunday. The preliminary X-rays did not show a fracture. But subsequent imaging revealed the small fracture.
The 49ers have eight regular-season games remaining on their schedule. Shanahan said the 49ers' medical staff is anticipating Kittle to be out of action for eight weeks.
"Kittle says two, but that’s how he rolls," Shanahan said. "But that’s why he’ll go on IR, and if it’s better than what they’re saying, he’ll have a chance to come back this year. But eight weeks is eight weeks."
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The 49ers hope veteran tight end Jordan Reed will be available to return to action Thursday night against the Green Bay Packers after missing the past five games with a knee injury. Reed returned to practice last week but remains on injured reserve. He is expected to be limited at practice on Tuesday evening.
The 49ers also will not have running back Tevin Coleman (ankle) or wide receiver Deebo Samuel (hamstring) available for the team's Week 9 game on Thursday night at Levi's Stadium, Shanahan said.