Philip Rivers, who missed practice Wednesday, is battling a back injury that is more severe than the team has acknowledged, a league source said.

Rivers' back injury was quietly added to San Diego's injury report last week, to go along with the rib injury he has been battling for weeks. By now, Rivers' rib injuries are improved, making his back injury the significant issue, a league source said.

Rivers has struggled in recent weeks, but he expects to play on Saturday at the San Francisco 49ers.

"At this point in the week I think there's no doubt," he said Wednesday.