It's unclear but apparently he's not traveling with the team so he's going to miss the road trip (BRK and HOU).
However, it sounds like he's been putting in work:
https://www.masslive.com/celtics/2021/03/boston-celtics-romeo-langford-enters-nba-health-and-safety-protocols.html
Langford has missed the first 36 games of the regular season after undergoing surgery on a broken wrist back in September. He has been progressing through plenty of on-court rehab in the past few weeks ahead of games, leading him to be fully cleared this week.
“He’s been looking great,” Marcus Smart said Wednesday. “He’s been putting the work in day in and day out. I know it sucks, it’s been six months since he played and been able to practice with us and things like that. That’s tough, especially when he’s the only one in the gym, having to work by himself and seeing everybody else working together and doing things like that. He’s dedicated himself to the work and I think it’s going to show up out there.”