Jefferson has taken most of the first-team reps in two-wide formations during training camp, Mike DeFabo of The Athletic reports.
Jefferson has "pole position" to be Pittsburgh's No. 2 wide receiver, according to Mark Kaboly of The Athletic.
The Steelers and Jefferson agreed to a one-year contract Friday, Brian Batko of the Pittsburgh Post-Gazette reports.
Jefferson caught 12 of 28 passes for 101 yards across 12 appearances for the Falcons in 2023. He caught eight of 15 targets for 108 yards in five appearances with the Rams.
Jefferson caught three of five targets for 19 yards during Sunday's 37-17 loss to the Bears.
Jefferson caught one of three targets for 13 yards during Sunday's 29-10 win over the Colts.
Jefferson didn't record a target during Sunday's 13-8 win over the Jets.
Jefferson caught one of two passes for 13 yards during Sunday's 24-15 win over the Saints.
Jefferson failed to secure his only target during Sunday's 25-23 loss to Arizona.
Jefferson caught one of four targets for 14 yards during Sunday's 31-28 loss to the Vikings.