Lacy already had been ruled out of Green Bay's game against the NFC North-rival Chicago Bears (1-5) on Thursday night.
NFL Media's Ian Rapoport noted that the injury is "more than an ankle sprain" and that a second opinion confirmed surgery was a necessity. ESPN's Adam Schefter also reported that Lacy will be headed to injured reserve, citing a source, prior to the team announcing the move.
Lacy is eligible to return to the club in Week 15.
Lacy, who was the only active halfback in Sunday's loss to the Dallas Cowboys, took to the air on two occasions in a bid to hurdle defenders in the contest. The 26-year-old bruising back played 31 snaps and rushed 17 times for 65 yards for the Packers, who are also without James Starks after the backup running back underwent meniscus surgery on Sunday.
Lacy, who will be a free agent in March 2017, has 71 carries for 360 yards this season. He has rushed 788 times for 3,435 yards and 23 touchdowns since being selected in the second round of the 2013 draft by Green Bay.
With two practices under his belt, Davis is expected to handle the rushing duties in Thursday's game versus the Bears.
The Packers also promoted running back Don Jackson from the practice squad. Jackson is an undrafted free agent out of Nevada.