Christian Kirk had barely settled into the San Francisco 49ers offense when the injury bug that has followed this receiver room all season found him again.

The 49ers placed the veteran wideout on injured reserve Saturday after he hurt the meniscus in his right knee during Thursday’s practice.

That keeps him out for at least four more games, and the team still hasn’t decided whether he’ll need surgery.

It’s his second trip to injured reserve in a little over two months. Kirk strained his calf on July 26, early in training camp, and that injury cost him the entire preseason and the first six games of the regular season.

He finally debuted in Week 7 in Atlanta, where he played 20 snaps in a loss without drawing a target. Two weeks later, he’s back on the sideline.

San Francisco signed him to a one-year, $6 million deal in March, expecting a reliable slot option, and so far he hasn’t been able to stay healthy long enough to be one.

Losing Kirk would be easier to absorb if he were the only one out, but he’s just the latest name on a long list.

Mike Evans is dealing with Achilles tendinitis on top of an earlier rib injury, and Deebo Samuel hasn’t played since hurting his hamstring against Seattle in Week 5.

General manager John Lynch said this week that neither Evans nor Samuel is likely to be available on Sunday.

The one piece of good news came alongside the Kirk move: Demarcus Robinson was activated off injured reserve after his own ankle injury, though he’s listed as questionable.

The 49ers also elevated KhaDarel Hodge from the practice squad, which tells you how thin the group has gotten.

Against the Raiders at Levi’s Stadium, Purdy’s receivers will likely be Brandin Cooks, Jacob Cowing, Jordan Watkins, a limited Robinson, and Hodge, all of them more comfortable as role players than as the top options in a Kyle Shanahan offense.

Kirk’s injury also leaves a specific hole. He was supposed to handle the short and intermediate routes over the middle, the kind of option-route work that lets Shanahan stretch defenses horizontally, and nobody left on the active roster does that naturally.

Expect George Kittle and the backfield to absorb a bigger share of the targets, with Purdy leaning on quick timing throws and play-action to get the ball out.

The 49ers are running low on designations to return players from injured reserve, so if they need those spots for others, Kirk might not come back at all this year.

For a team that still sits atop the NFC West, the next month will show whether Shanahan can keep the offense functioning with whoever is healthy, or whether the front office has to look outside the building for help before it’s too late.