War of attrition affecting 49ers already

San Francisco 49ers quarterback Jimmy Garoppolo (10) huddles with the offense during the game against the Detroit Lions.Photo: Sergio Estrada-USA TODAY Sports

Coach Shanahan: "You hope to weather the storm and get through it."

The San Francisco 49ers have lost their starting quarterback for the season. Both their starting wideouts are banged up, and their top running back has been in and out of the lineup with a shoulder injury.

It seems the only things they can count upon these days are their tight end and offensive line.

And now that's only half-true.

Following a third loss in four games, the 49ers went back to work Wednesday with three starting offensive linemen watching from the sidelines -- center Weston Richburg and tackles Joe Staley and Mike McGlinchey -- all dealing with knee injuries.

All three injuries occurred in the Week 3 loss at Kansas City, although Richburg was able to play the entire game, while McGlinchey missed just three snaps.

Staley was helped off the field in the second quarter and could not return.

Asked what his starting line would be if the upcoming game against the Arizona Cardinals had been Wednesday, 49ers head coach Kyle Shanahan used simple math.

"How many left after those three? I think there's seven left," he said. "So it'll be five of those seven."

The seven at practice Wednesday were center Erik Magnuson, guards Laken Tomlinson, Mike Person, Joshua Garnett and Najee Toran, and tackles Shon Coleman and Garry Gilliam.

Even those seven had their issues. Person injured his knee in the opener at Minnesota and hasn't been 100 percent since. Garnett left the opener with a dislocated toe and Wednesday was his first practice (no games) since. Toran was an in-season addition to the practice squad, while Coleman hasn't played a down since being acquired by the 49ers on the eve of the opener.

Oh, one more thing: The blitz-crazy Cardinals are coming to town.

Shanahan noted that no matter who lines up in front of him, the onus is on replacement quarterback C.J. Beathard to identify what's coming at him and attack accordingly.

"He played in a number of games last year where the (offensive) line was pretty beat up," Shanahan said of Beathard, making that experience sound like a positive. "I think he's gotten better knowing where people are, faster with it. That happens the more you play in a system. So he's much further ahead this year than he was last year."

Despite the absence of Jimmy Garoppolo, Richard Sherman and a handful of others, the 49ers came a play or two from winning in Los Angeles against the Chargers in Week 4.

Shanahan's take-away from the game: His team is good enough to beat anybody, as long as it can prevent going into games at a mental disadvantage.

"It's the biggest challenge I think in our game," he said of dealing with injuries. "It's a challenge that a lot of people deal with, that I've had to deal with in my career before. It has been a little bit different these two years in some situations that I haven't been in prior. Chalk a lot of that up to just luck.

"I know the fortunate thing is, not counting our quarterback and our running back, all of the (offensive) linemen ... they're not going on (injured reserve). They will return eventually, hopefully sooner than later.

"Some years you have lucky years. My last year in Atlanta, I don't think we had one guy hurt on offense the whole year. It doesn't always pan out that way. You hope to weather the storm and get through it and win some close games, and you hope to get healthier as it goes, just like we did last year."

SERIES HISTORY: 54th regular-season meeting. 49ers lead series, 29-24. The Cardinals have won the last six meetings, including 20-10 in last year's visit to Levi's Stadium. The 49ers' last home win over the Cardinals was 20-17 in December of 2014. The clubs have never met in the postseason.