SANTA CLARA — Mario Manningham limped through the locker room on crutches, holding a towel around his waist while trying to keep his head high and sport a smile.
That's not easy to do for the San Francisco 49ers right now.
Manningham is out of the season with a left knee injury after getting tackled low by Leroy Hill and fumbling in the third quarter of San Francisco's 42-13 loss at Seattle. The injury to Manningham, one of San Francisco's signature additions in the offseason, is yet another blow to an increasingly thinning wide receiver corps.
Kyle Williams already is lost for the season with a left knee injury and tight end Vernon Davis did not participate in Wednesday's practice while he recovers from a concussion. Davis took a huge hit from Seattle's Kam Chancellor and must be cleared by an independent neurologist before he can return.
With so many injuries to key receivers, the 49ers (10-4-1) will rely more than ever on Randy Moss and first-round pick A.J. Jenkins to support top threat Michael Crabtree, starting Sunday against the Arizona Cardinals (5-10) in the regular-season finale. Niners coach Jim Harbaugh also said Ricardo Lockette or Chad Hall will likely be promoted from the practice squad.
"That group will have to step up," Harbaugh said.
The loss of Manningham is a significant setback for a team that counts on Crabtree as its only healthy wide receiver with more than 26 receptions this season.
Crabtree has 77 receptions for 933 yards and seven touchdowns. Manningham's over-the-shoulder catch between two defenders on the sideline in the Super Bowl propelled the New York Giants' winning TD drive against the Patriots last February. He ranks second with 42 catches for 449 yards and a touchdown after missing some time previously with a shoulder injury.
After those two, San Francisco has received limited production from its other wide receivers.
Moss, two months shy of his 36th birthday, has 26 receptions for 406 yards and three touchdowns. Ted Ginn Jr., has two catches for 1 yard. And Jenkins, drafted 30th overall out of Illinois, has been active for three games and has not been targeted.
About the only positive for San Francisco is that second-year quarterback Colin Kaepernick often worked with the backups and practice squad players before being promoted over Alex Smith six weeks ago.
"I think that's why we're not too worried about it," said Kaepernick, who is 4-2 since taking over for Smith. "I've had a lot of practice with those other guys."
Just not when it counts.
Jenkins couldn't crack the lineup at the outset with Crabtree, Manningham, Williams and Moss ahead of him on the depth chart — not to mention Davis, Delanie Walker and the other tight ends in Harbaugh's complicated version of the West Coast offense. Frank Gore also has 25 catches for 213 yards out of the backfield.
At the most important time of the season, now it's Jenkins and other wide receivers with little experience suddenly being thrust into a bigger role.