The team announced Porter won't return after being diagnosed with back spasms. Garrett Temple took his spot in the starting five for the second half.
Porter appeared in each of Chicago's first 10 games this season. Friday marked his sixth start. He is averaging 14 points and 6.9 rebounds per game to start the 2020-21 campaign.
Porter, 27, had an injury-plagued 2019-20 season, appearing in the team's first nine games before a foot setback sidelined him for four months. That was a major blow for a Bulls team that entered the season with high aspirations but started just 3-6 before Porter's injury.
Porter was supposed to be one of the team's core pieces alongside Lauri Markkanen, Wendell Carter Jr. and Zach LaVine. He was excellent in 2018-19 for the Bulls after they acquired him in a midseason trade with the Washington Wizards, averaging 17.5 points, 5.5 rebounds and 1.2 steals per game while shooting 48.3 percent from the field and 48.8 percent from three.
But staying on the court has remained an issue, limiting Chicago's upside. While he's out of action, look for Temple and Thaddeus Young to see more minutes for the Bulls.