Mario Manningham missed his third practice of the week, and Jim Harbaugh said the receiver, who has started nine games this season, is listed as doubtful on the 49ers' injury report. That means rookie receiver A.J. Jenkins likely will see his first snaps of the season, Harbaugh said. "He's been on his assignments, he's executed well when he's been out there," Harbaugh said. "He's giving great effort. Football rewards that effort."