Horford has been out since suffering the injury Dec. 26. He had surgery to repair the torn muscle four days later.
Kent Bazemore, who has been limited coming off foot surgery, also took part in the five-on-five scrimmage for the first time in training camp.
Hawks coach Mike Budenholzer said the plan is still to be cautious to ensure each player is ready for the season opener on Oct. 29.
“Each day they are making a little bit of progress,” Budenholzer said. “You always want to evaluate them to see how they come back the next day. You might even intentionally do a little bit less. We’ll see how they feel. But I think, luckily, they seem to be making the appropriate steps and progress that we want them to make.”