The 49ers placed Jackson on the reserve/PUP list with a knee injury, Field Yates of ESPN reports.
Head coach Kyle Shanahan told reporters Monday that Jackson (knee) isn't expected to return during training camp, Lindsey Pallares of the 49ers' official site reports.
The 49ers placed Jackson (knee) on the active/PUP list Tuesday, David Lombardi of The Athletic reports.
Jackson (knee) was placed on injured reserve by the 49ers on Saturday, Matt Barrows of The Athletic reports.
Jackson (knee) has been ruled out ahead of Sunday's game against the Jaguars, Nick Wagoner of ESPN.com reports.
Jackson recorded three sacks during Sunday's 30-7 win over the Steelers.