The star shooting guard has been playing through a non-displaced fracture in his lower back, NBC Sports' Dwight Jaynes reports.
McCollum suffered the injury during Portland's first game of the restart against the Memphis Grizzlies when he took a knee to his back from Jaren Jackson Jr., sources told TNT's Chris Haynes.
Despite struggling for much of Tuesday's thrilling 134-131 win against the Dallas Mavericks, McCollum knocked down a pair of free throws to extend Portland's lead to three points heading to the game's final possession. The 28-year-old finished the game with eight points on 2-of-14 shooting.
The Trail Blazers' latest victory moved them ahead of the Memphis Grizzlies for sole possession of the Western Conference's eighth seed.
Portland can clinch its spot in the West's play-in tournament with a win over the Brooklyn Nets on Thursday.