The Pacers selected Sumner in the second round of the 2017 NBA Draft out of Xavier University. He appeared in just one game during his rookie campaign, but he has since earned a larger role in Indiana.
Sumner played the most games of his professional career last season for the Pacers, averaging 7.5 points and 1.8 rebounds in 16.2 minutes per game across 53 contests (24 starts).
The 25-year-old Sumner shot 52.5% from the field and 39.8% from 3-point range.
This isn't the first major injury for the 6-foot-4 point guard. Sumner also tore his left ACL early in 2017 during his sophomore season at Xavier.
With the injury, the Pacers are down to three point guards on their roster: Malcolm Brogdon; T.J. McConnell and Duane Washington Jr.
Indiana is set to begin its regular-season schedule Oct. 20 against the Charlotte Hornets.