SANTA CLARA — The 49ers on Monday placed starting defensive end Tank Carradine on injured reserve with a high-ankle sprain.

Carradine was on crutches and in a walking boot over the weekend after being injured in the second half Thursday against the Rams. He writhed in pain for more than a minute before being helped to his feet. He walked slowly off the field.

The injury is expected to keep him out for at least four weeks. The 49ers can move up to two players from injured reserve back to the active roster, but those players must be inactive for eight weeks.

Another defensive end, Ronald Blair, currently is on injured reserve with a broken thumb. Both Blair and Carradine play the so-called “big end” position for San Francisco. First-round draft pick Solomon Thomas likely will start while Carradine is out. Thomas, who also plays inside on passing downs, has played 128 defensive snaps this season and Carradine 81.

San Francisco used Carradine’s roster spot to sign linebacker Mark Nzeocha off the Dallas Cowboys’ practice squad. Nzeocha was drafted by the Cowboys in the seventh round in 2015. He played in eight games and recorded four tackles. Dallas waived him Sept. 3 and then signed to the practice squad.

A 27-year-old native of Ansbach, Bavaria, in Germany, Nzeocha attended Wyoming.

One of the 49ers’ inside linebackers, Reuben Foster, is out with a high ankle sprain and likely will miss at least one more game. Another, Brock Coyle, suffered a concussion in Thursday’s loss to the Rams.

Carradine, 27, performed well in his first season as a starter. He has one of the 49ers’ three sacks this season to go along with seven tackles. He is entering the final year of his contract.

The 49ers rank 30th in the league in sacks through three weeks. Only Tampa Bay — one sack — has fewer, but the Buccaneers have played just two games because of Hurricane Irma. The 49ers rank 18th in total defense, having allowed 339 yards a contest. Last year, they gave up an NFL-worst 406.4 yards per game.