SANTA CLARA -- All-Pro defensive tackle Justin Smith was not on the 49ers' field at the beginning of practice Thursday, casting serious doubt whether he will be available Sunday night to face the Seattle Seahawks.
Smith played the first four snaps of the second half against the New England Patriots before leaving the game with a left elbow injury. Coach Jim Harbaugh has been vague while discussing Smith's condition, saying only that Smith will play "if it's humanly possible."
Injured players have spoken privately about receiving warnings from the team about disclosing their injuries to the media. After Sunday's game, Smith said he could not comment on his condition. He underwent an MRI examination on Monday. Late in the exhibition season, the 49ers withheld the extent of outside linebacker Parys Haralson's injury before placing him on injured reserve with a torn triceps.
Smith's situation appeared serious Sunday night, as he could not return to play in the second half. The Patriots scored touchdowns on four consecutive drives without Smith on the field in the third and fourth quarters.
"Obviously, anytime you lose a great player, it's going to have an effect on you," 49ers defensive coordinator Vic Fangio said. "You'd have your head in the sand if you didn't admit that. I think some of the issues we had, plays we could've stopped, didn't have any effect with him being out there."
Fangio said backup defensive lineman Ricky Jean Francois is ready to fill in. Jean Francois ended a Patriots drive late in the game with a sack of Tom Brady.
"He can play both the banging game and got a little bit of athleticism, too," Fangio said. "He's a well-rounded player. He's the one guy in our front who can play all three spots. Nothing will change with him in there."
Safety Dashon Goldson said the entire 49ers defense will have to compensate for the potential loss of Smith.
"We definitely have some guys going to have to step up and carry that load for us," Goldson said.