San Francisco 49ers strong safety Michael Lewis sustained his third concussion of the season, going down early in the third quarter of Sunday's 45-10 loss to the Atlanta Falcons while trying to tackle running back Michael Turner.
Lewis, who sustained two concussions during an 11-day span during the preseason, could be sidelined for a prolonged period.
Lewis led with his helmet on the hit Sunday and was face down on the field for several minutes while being examined. He eventually sat up and was helped off the field, appearing dazed. Athletic trainers ran a series of tests on Lewis as he sat on the sideline.
Lewis' first concussion occurred Aug. 18 during a joint practice with the Oakland Raiders at their Napa, Calif., training site when he was hit by a fullback. Lewis suffered another concussion during an Aug. 29 preseason game at Dallas when he fell and took a knee to the helmet.
The Associated Press contributed to this report.