The team signed fullback Owen Schmitt and tight end/fullback Garrett Mills to fill the roster spots.
Weaver and Jackson were injured in Sunday's 27-20 loss to Green Bay.
Schmitt, a fifth-round draft choice by Seattle in 2008, played in 30 games with the Seahawks. He caught 12 passes for 50 yards and one touchdown, and carried five times for 21 yards. Schmitt was released on Sept. 6.
Mills had been on Philadelphia's practice squad. Guard Fenuki Tupou agreed to a contract and will take Mills' spot on the practice squad.
Weaver tore the anterior cruciate ligament in his right knee. Coach Andy Reid called the damage to his knee "severe," and said a surgery date for Weaver hasn't been set.
Jackson tore his right triceps, not biceps as the team originally said. He will have surgery on Tuesday. Jackson was in the starting lineup after making a remarkable recovery from surgery to repair a torn ACL sustained last Dec. 27.
Reid said both players must pass a specific evaluation process before they are cleared to play. He said the team's medical staff will follow the NFL's guidelines for concussions.
Both players briefly returned after getting hurt in the second quarter against the Packers.