49ers’ place Drake Jackson on injured reserve, will be out at least four games

Defensive end Drake Jackson, a former second-round draft pick who opened the season with a three-sack game against Pittsburgh, was placed on injured reserve Saturday and will miss a minimum of four games.

Jackson had seen his playing time dip significantly in his last four games after opening the season on a rotation basis with Clelin Ferrell opposite Nick Bosa. He played just 10 snaps in the 49ers’ 31-17 loss to Cincinnati before the bye and was declared out of Sunday’s game with Jacksonville because of a knee injury.

After four games, the 49ers could choose to activate Jackson to the active roster or leave him there for the remainder of the season. With the acquisition of Chase Young last week by trade from Washington, Jackson could have conceivably been inactive against Jacksonville even if healthy.

After fading during his rookie season a year ago, Jackson, along with Javon Kinlaw, drew raves for their offseason and training camp work by the coaching staff. Jackson, in particular, was praised by the coaching staff for remaking his body after being a healthy scratch in four of the 49ers’ last five games (including the playoffs) a year ago.

Jackson had three sacks in a season-opening 30-7 win over Pittsburgh and played 28, 40, 30 and 41 snaps in the first four games. In the last four, Jackson’s snap count dropped to 28, 30, 15 and 10.

Cornerback Shemar John-Charles was activated from the practice squad to assume Jackson’s roster spot. The two standard practice squad promotion for the Jacksonville game are wide receiver Willie Snead IV and linebacker Curtis Robinson.