Collins will miss the Tigers' game on Saturday against Notre Dame.
Collins was ejected on Thursday after he undercut Duke guard Wendell Moore from behind while Moore was in midair on a breakaway dunk. Moore fell from the rim, landing hard on his back. Mike Krzyzewski immediately went onto the court, but Collins was given a flagrant 2 and ejected, with no further incidents from either team.
Before leaving the court, Collins and Clemson coach Brad Brownell went over to Krzyzewski to apologize, with Collins and Krzyzewski hugging.
"Brad's an old-school, damn good coach and good guy. He's good people and his kids are good people," Krzyzewski told reporters after the game. "We didn't want that to escalate, so the fact that he brought him and we did some interaction, I think that was really good. And you put it behind. Brad apologized, I said, 'Please, let's just move on.' ... It was best to move on."
Collins posted an explanation and apology on his Instagram on Thursday night.
"I was going to try to block it from behind but I was going too fast and I couldn't stop," Collins wrote. "I realized I needed to stop when it was too late I never have been a dirty player never will I wish bro a healthy season and I never tried to hurt anybody but I know everyone is entitled to their own opinion I have respect towards Duke and Clemson and I apologize to everybody for a reckless play I'm glad Wendell is okay."
Duke won Thursday's game 82-64.
Collins, who transferred to Clemson from South Florida last spring, is averaging 10.5 points and 6.7 rebounds this season.