Also ruled out are running back
The Chargers are 1 1/2-point underdogs.
"A ball did not hit the ground in all the throws he made today," McCoy added. "Philip was Philip, so he'll be ready to roll."
Rivers was a full participant in Thursday's practice after sitting out Tuesday and Wednesday. He should be ready to roll for Saturday's matchup with the 49ers.
Rivers has thrown one or zero touchdowns in five of his past six games. The Chargers are 1-point underdogs at San Francisco.
"I hate not practicing," he told ESPN.com. "But I think at some point you have to do what's best for me and the team. And practicing [Wednesday] wouldn't have been beneficial to moving toward Saturday."
Added Rivers about his playing status: "At this point in the week, I think there's no doubt."
If Rivers surprisingly sits out, backup
"One of the reasons we brought Kellen in here is that he was very competitive last year, thrown into a tough situation," offensive coordinator Frank Reich told the website. "He played well against some really tough defenses. He's a very smart competitive guy."
The Chargers are 1-point underdogs at San Francisco.