Indiana Pacers forward Glenn Robinson III will undergo surgery on his injured left ankle and is expected to be out of the lineup until mid-December, league sources told ESPN.

Robinson had missed most of training camp and the preseason with a high ankle sprain, and the necessity now for a surgical procedure will extend his original two-month timetable on a return for an additional two to four weeks, league sources said.

Robinson suffered the injury Sept. 29 in a scrimmage during practice, crumbling to the floor after a drive to the basket.

The Pacers consider Robinson, 23, a key part of the franchise's rebuild and plan a prominent role for him in the post-Paul George era.

Robinson, the 2017 NBA Slam Dunk champion, blossomed into a solid contributor last season. He averaged a career-high 6.1 points and 3.6 rebounds in 20 minutes per game. Robinson shot nearly 40 percent from the 3-point line.

After leaving Michigan following his sophomore season, Robinson was a second-round draft pick who had stops with the Minnesota Timberwolves and Philadelphia 76ers, before landing with the Pacers for the 2015-16 season.