SEATTLE -- Tight end Vernon Davis and wide receiver Mario Manningham sustained serious injuries that knocked them from the 49ers' 42-13 loss Sunday night to the Seattle Seahawks.
Davis left with a first-quarter concussion and the 49ers trailing 14-0. That deficit had grown to 28-6 by the time Manningham suffered a third-quarter knee injury.
Davis' injury occurred when he got leveled by safety Kam Chancellor on a potential first-quarter reception at the Seahawks' 2-yard line. Coach Jim Harbaugh said Davis informed him it's a "mild" concussion and that "he said he felt better."
Chancellor drew a 10-yard, unnecessary-roughness penalty, and the 49ers thus had first-and-goal at the 10-yard line. The series ended with Richard Sherman's 90-yard touchdown return of a blocked, 21-yard field goal attempt by David Akers.
Davis, who's started the past 90 games dating back to 2007, made a 27-yard catch earlier in the drive to bring the 49ers into Seahawks territory for the first time.
Manningham injured his left knee while being tackled on the 49ers' opening series after halftime. Linebacker Leroy Hill drove his helmet into Manningham's knee on the reception, which Manningham then fumbled at the Seahawks' 40-yard line.
Harbaugh said X-rays were negative on Manningham, who missed the previous two games because of a shoulder injury.
Asked if Smith indeed could return for the playoffs, Harbaugh said: "I really don't know."
Smith did not practice last week after injuring his left elbow in the 49ers' 41-34 win at New England on Dec. 16. Ricky Jean Francois started in place of Smith, who was in attendance and wore no visible arm brace.
"Not having Justin is a huge deal," safety Donte Whitner said. Added linebacker Ahmad Brooks: "You felt it all week. It just felt different. You always hear him out there."
Asked how Justin Smith's absence affected him, Aldon Smith said: "I wouldn't say I was doubled more. They saw Justin was not there and they tried to take advantage of it."
Sherman started at cornerback two days after reportedly attending an appeal hearing in New York regarding a potential four-game suspension for performance-enhancing drug use. After the game, he said there was a "chain of custody" mistake that led to his positive test and was the basis of his appeal.
The Associated Press contributed to this report.