Portis was suspended eight games by the organization for punching Mirotic in the face during Tuesday's practice, leaving the power forward with a concussion and facial fractures that will require surgery.
Head coach Fred Hoiberg wouldn't elaborate on what Portis said to his players, but did admit that it was positive to see him on the floor during Friday's practice.
"It was good to have him back in here," Hoiberg said. "Obviously everybody's looking forward to getting Niko back in here as well, hopefully soon.
"His (Portis) spirit was good. Right now, our job is to get the guys out there that we have and get them prepared to play different positions than they've been playing. So he didn't get a lot of reps out there today. It was really a shorter, correcting, teaching-type practice."
Mirotic is expected to miss the next four-to-six weeks recovering from his injuries.
Portis will be eligible to return to action Nov. 7 at the Air Canada Centre against the Toronto Raptors, who Chicago fell to in the season opener on Thursday, 117-101.