The Blazers accidentally submitted a roster with McCollum on the inactive list instead of teammate Luis Montero, whose name appears next to McCollum's alphabetically on the sheet teams must submit before the game. For Portland, which has 15 players on its roster, the sheet lists 13 active players and two deemed inactive.
The Blazers' public relations team described the mistake as a "clerical error."
Due to a clerical error in the NBA's active list reporting, CJ McCollum is inactive for tonight's game vs. LAC. Luis Montero is active.
— Trail Blazers PR (@TrailBlazersPR) January 7, 2016
Afterward, Blazers coach Terry Stotts took full responsibility for the error.
"I signed the paper without really noticing it, but it's my fault for not looking at it," Stotts said. "Although we caught the error, we thought we'd caught it in time, apparently we did not, so C.J. was ruled inactive, and that's that.''
But that may not have been that. McCollum still may have been able to play if Clippers coach Doc Rivers had agreed to that option. Rivers, however, declined, according to the Oregonian, citing a league source.
"We were trying to figure out what the heck," Rivers said. "We knew you couldn't change the rule, because it happened to us. But it's not on us to do that. That's all on them."
McCollum said he was putting the issue behind.
"It's unfortunate, but it's over with," he said. "Just moving on to the next game."
Had the Blazers attempted to play McCollum, they would have been assessed a technical foul and he would not have been allowed to play. In 2007, the then-Charlotte Bobcats were penalized for playing Jeff McInnis, who was ineligible. The same happened to the Washington Wizards in 2010, when they played Roger Mason.
The Clippers mistakenly left Danny Granger off the active list in a March 2014 game against the Pelicans, and he had to sit.
"We've made that error twice in the last two years," Rivers said. "One we had just signed a guy right before the game."
Rivers also questioned the process.
"There should be no 'active list,'" he said. "I've been fighting this for three years. If someone can explain to me why there is an active list, I'd love to hear it. We can't get it changed, and as coaches it's tough."
After beginning the game in uniform on the bench, McCollum changed into street clothes during the second quarter. McCollum, who averages 21.0 points per game and entered Wednesday sixth in the NBA with 89 3-pointers, was replaced in the starting lineup by Allen Crabbe, who finished with 11 points on the night.
Information from The Associated Press was used in this report.