Niners coach Kyle Shanahan on Friday said defensive tackle D.J. Jones will land on injured reserve Saturday with an ankle injury, ending his season.
Jones was already playing on an injured ankle and suffered a high sprain on his other ankle against the Saints, Shanahan said. Jones played through the injury but it was discovered to be more serious upon further testing.
"That was what was pretty impressive," Shanahan said. "That's why we were somewhat optimistic about it. He did it early in the game, too, maybe the first drive. But that's why we were optimistic. But after they looked in there and stuff, it was too bad and it was going to be more likely eight weeks."
While Jones doesn't get the acclaim of the Niners' other three starting defensive linemen, he has been an integral piece of the group, doing the dirty work by taking on double-teams and stuffing the run.
Jones started all 11 games in which he appeared this season, posting 23 tackles and two sacks. He previously returned from spraining his other ankle.
Jones joins cornerback Richard Sherman (hamstring), defensive end Dee Ford (hamstring), cornerback K'Waun Williams (concussion) and center Weston Richburg (patellar tendon) among those who suffered injuries against the Saints and will miss at least this week's game.
Richburg is out for the season, while Sherman and Ford are being viewed as week-to-week.
Shanahan said the nature of hamstring injuries usually means anywhere from two to four weeks, and Sherman said Thursday he could have played this week if necessary and is aiming to return sooner rather than later.
Taking Jones' spot on the roster is defensive lineman Kentavius Street, who will be designated to return from injured reserve on Saturday.
Street was a 2018 fourth-round draft pick out of North Carolina State, but he has yet to appear in a game for the Niners. He sat out last season after tearing his ACL in the pre-draft process and then had a setback this year when he was forced to have arthroscopic surgery on his knee, landing on injured reserve.
The 49ers opened Street's practice window last week and feel good enough about him to activate him for Sunday's game against the Atlanta Falcons. Street had played inside and outside for the Niners, but he is focused on inside now given the opportunities for snaps there.
"Ideally, he's probably more of an inside guy," defensive coordinator Robert Saleh said. "Of course, rotation and injuries will always dictate where he plays, but we feel like he's got a chance to be a pretty good football player on the inside, whether it's at the nose or 3-technique. Working to make sure he gets as much work at that as possible, but understanding that with the attrition that we've been having at the D-line, that we may have to flex him if he gets those opportunities."