While last week's MRI didn't reveal any significant damage, head coach Kyle Shanahan said on Thursday that it didn't come back completely clean.
"There's issues," Shanahan told reporters. "So, yes. He's got things in his knee and ankle, so we'll see."
Kittle did not practice on Thursday, and the 49ers probably won't know his status until closer to game day.
General manager John Lynch joined KNBR on Friday morning and was asked about his level of concern for his Pro Bowl tight end.
"Well, first and foremost, I just felt incredibly blessed for everybody that he was okay," Lynch said on the "Murph and Mac" show. "I'm sitting there on [Thursday] night, and I've got the luxury of having a replay right over me. And as I saw that, I said, 'Oh no.' I mean, that did not look good the way that knee hyperextended. And then next thing you know, Kittle is in there doing what he does — breaking loose and busting loose."
Lynch admits that much of that return performance following the injury probably had to do with adrenaline, and the team will see if he can return to the practice field on Friday or Saturday.
"He injured both his knee and ankle," Lynch continued. "I think the prognosis is good in terms of nothing long-term, and we all know, with George, he's as tough as they come. He wears these trainers out. He's here from morning 'til night. He's doing his best because every game is a huge game for him."
Added Lynch: "We're hopeful, but I can't say more than that because I just don't know yet."
You can listen to the entire conversation with Lynch below.