Kristaps Porzingis on Monday moved one step closer to a return to the Celtics lineup.

The rehabbing Boston man reached the “next phase of his recovery” from offseason leg surgery, the team announced.

As part of that phase, Porzingis and forward Xavier Tillman were briefly assigned to Maine in order to practice with the Celtics’ G League affiliate on Monday. After the practice, which was held at the Celtics’ Brighton facility, both players would be recalled to the NBA roster, “where Porzingis will continue to ramp up his workload.”

The team did not offer an updated timeline for Porzingis’ return. The latest reports indicated he and the Celtics were targeting December for his season debut.

The Celtics also did not specify why Tillman joined Porzingis for his G League practice, but he’s fallen out of their rotation of late, logging just 19 total minutes over Boston’s last nine games.

After spending most of the offseason in his native Latvia, Porzingis has been around the Celtics since training camp began. Last week, he traveled with the team to its road win over Brooklyn, where he ran through an extensive pregame workout before watching the game from the bench in street clothes.

“I think that’s important, especially for a guy that’s not playing, to be as engaged as he is,” head coach Joe Mazzulla said after that game. “It makes it easier for as he starts to come back we’ll just plug him right in, because he’s been here the whole time. That’s a commitment. That’s hard to sit there day in and day out and do that. So I appreciate that he does that. I think it brings a level of professionalism and togetherness to our locker room, and it’s been fun to watch.”

Porzingis also has upped his workload in practice.

“Even just doing little drills here with him today, he just makes the game so much easier with his length, being able to protect the rim,” guard Jrue Holiday said last Friday. “And then, obviously, offensively he just makes the game so much easier for everybody. Creating space for driving lanes or 3-point shots. Not being able to switch off of him or when he gets a switch, him being able to take advantage of that. Can’t wait for him to come back.”

The Celtics are off to an 11-3 start without Porzingis, but they’ve missed his rim protection at times. They’ll host the 15-0 Cleveland Cavaliers on Tuesday night in a battle of Eastern Conference front-runners.