Tim Rattay will make his first NFL start in place of Garcia, a three-time Pro Bowler who has struggled with several injuries all season. He has a partially torn ligament around his sprained ankle, and team doctors strongly recommended at least a week of rest.
"It has been a nagging injury holding me back every single week," Garcia said Thursday. "Hopefully this will give me an opportunity to somewhat heal up, but it was not really what I was looking forward to, not what I was hoping for."
Garcia's streak of 61 straight starts, fifth longest among active quarterbacks and the longest in San Francisco history, would end Sunday. The 49ers have their bye week after the game, followed by a Monday night game against Pittsburgh.
Rattay, a fourth-year pro, has played sparingly as Garcia's backup the past three seasons. He is 15-of-24 for 162 yards and a touchdown while playing in four games this season.
Coach Dennis Erickson made his decision early to give Rattay plenty of time to prepare.
"(Garcia) just can't move, so there's no reason to put him out there without his mobility," Erickson said. "It doesn't change anything we do as far as our game plan is concerned. Our game plan is fit for both guys."
Rattay, who signed a contract extension with the 49ers shortly before the season, worked with the 49ers' first-string offense in practice this week. With Garcia's up-and-down health this season, Rattay figured he would eventually get a chance to fill in for his friend.
"This week is nice because I get the reps in practice, so I get to see the different plays unfold instead of just standing and watching," Rattay said. "Mentally, I have to prepare like I'm going to play every week regardless. Obviously, it's easier when you know you're going to play to prepare yourself mentally."
Erickson doesn't plan any reduction of the 49ers' game plan to accommodate Rattay, and there will only be minor changes in strategy.
"He can throw it. He's got a good arm," Erickson said. "He understands the game. He knows this offense, he's been around, so now he has an opportunity to step up and play. I have all the confidence in the world in him."
Nobody questions the toughness of Garcia, who has played through numerous injuries during his five seasons with the 49ers. He hurt his back while lifting weights during the summer, forcing him to miss much of training camp, and he also sustained several minor injuries to his ankles and arms that didn't prevent him from playing.
"I did take a lot of pride in being out there every single weekend to contribute and help the team compete at the highest level," Garcia said. "It's hard for me to sit here and say that that's coming to an end."
Garcia's health was improving until last week's 16-13 loss to Arizona, when he sprained his ankle and missed several series. He rushed for two touchdowns against the Cardinals, but couldn't get the 49ers in the end zone late in the game.
"When I look at it, it's an ankle sprain," Garcia said. "When they look at it, it's torn ligaments and strained ligaments and strained muscles and all those things that come into play."
Garcia was held out of practice Wednesday, but the 49ers often rest their offensive stars during the week. The quarterback attended a Sacramento Kings game Wednesday night with three of his offensive linemen, and he didn't appear to be particularly hobbled.
Garcia has passed for 1,523 yards with eight touchdowns and eight interceptions. His passer rating is a dismal 72.0, and he hasn't rallied the 49ers (3-5) to any of the comeback victories that have been his specialty.
Garcia has been the 49ers' full-time starter since winning the job late in the 1999 season. He played five seasons in the CFL with the Calgary Stampeders before joining San Francisco.
He led the 49ers to consecutive playoff appearances over the last two years, including a dramatic comeback victory over the New York Giants last season.
Garcia's absence is the biggest blow yet for the 49ers' struggling offense, which has dealt with injuries on the offensive line and the declining production of All-Pro receiver Terrell Owens, who has criticized Garcia this season.
This story is from ESPN.com's automated news wire. Wire index
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