As a result, he will miss at least four weeks before being re-evaluated.
The 29-year-old was off to a roaring start through the first part of the season, averaging 26.7 points, 5.0 assists and 3.9 rebounds through 13 games before suffering the injury against the Atlanta Hawks on Saturday.
McCollum has emerged as one of the top playmakers for Portland since his early days in a bench role. Over the past five seasons, he has appeared in at least 70 games and averaged 21.5 points per season.
McCollum is the second key player to land on the injured list for Portland in the past two weeks, joining center Jusuf Nurkic.
Shams Charania of The Athletic and Stadium reported that Nurkic was expected to miss eight weeks after suffering a fractured right wrist last week.
Now, a Blazers team that is off to an 8-6 start will have to battle to remain in the playoff race.
Without the Lehigh product, the Blazers will look to Gary Trent Jr. and Rodney Hood. Trent has averaged 10.8 points per game through 12 outings, while Hood has averaged 14.1 minutes per game.
Point guard Damian Lillard will also be asked to produce even more from a scoring perspective and figures to put up monster numbers during McCollum's absence.