Team sources tell ESPN that Rivers is playing with a bulging disk in his lower back that doctors fear is on the brink of being herniated.
The disk caused Rivers to miss practice Wednesday for the first time since 2007 even though the injury began to bother him some three weeks ago.
Rivers has taken epidural injections to reduce swelling, according to sources. He hopes to avoid offseason surgery, but it is an option, according to sources.
Rivers finished 33-for-54 for 356 yards in Saturday's38-35 overtime victory that helped keep the Chargers' playoff hopes alive. Although he threw three interceptions, he threw four touchdown passes andconverted fourth-and-8 and fourth-and-10 on San Diego's final drive of the fourth quarter as the Chargers rallied to win after trailing by 21 points at halftime.
49ers Lose 21-Point Lead, Lose To Chargers
SportsCenter Highlight of the Night: Despite 355 rushing yards and three touchdowns from the 49ers, Philip Rivers and the Chargers came back from a 28-7 deficit to beat San Francisco 38-35 in overtime.
Game Balls: 49ers vs. Chargers
ESPN Chargers reporter Eric Williams' game ball goes to quarterback Philip Rivers, who passed for 356 yards and four touchdowns while throwing three interceptions. With 158 rushing yards, Niners running back Frank Gore gets Paul Gutierrez's game ball.