Also, the Globe article linked below seems to indicate that Tatum is improving:
www.bostonglobe.com

Jayson Tatum says he’s still experiencing side effects from his bout with COVID-19 - The Boston Globe
The Celtics forward said Tuesday that he has had some respiratory issues. “I think it messes with your breathing a little bit,” he said.

EDIT: LTP got in a minute earlier, but the point still stands.“It’s just certain stretches where breathing is a little out of whack, and I talk to the medical staff and coaching staff about it,” he said. “It’s gotten better obviously from the first game I came back and played.