Celtics rookie JD Davison’s marching orders? Talk to Marcus Smart.

Rookie point guard JD Davison signed a two-way contract with Boston last summer.Matthew J. Lee/Globe Staff

Celtics rookie point guard JD Davison is fast, athletic and physical, and he has the tools to become a high-level defender in the NBA. But Davison, who turned 20 on Monday, remains in the nascent stages of learning the nuances of the game at the highest level.

So in recent weeks, coach Joe Mazzulla, in addition to offering his own instruction, has pointed Davison toward one of the team’s most indispensable resources.

“He basically tells me, ‘Talk to [Marcus] Smart,’” Davison said Tuesday. “I talk to Smart a lot.”

Smart, the reigning NBA Defensive Player of the Year, has been a willing teacher, and Davison has been almost awestruck by how his fellow point guard conducts the team at that end of the floor.

“Definitely on the defensive end, you can see why they were the No. 1 defense in the league last year,” said Davison, the 53rd pick of last June’s draft. “So you see you’ve got to come here and learn and pick up everything on the defensive end. Marcus is teaching me everything that he knows, so just learning from him, that’ll be big for me.”

Davison said he has also been leaning on other veterans such as Jayson Tatum, and he acknowledged that they tend to initiate the instruction, because he is not always comfortable asking for help yet.

Davison looks for an opening during a summer league game earlier this year.John Locher/Associated Press

But he is eager to keep learning and growing. Davison, who signed a two-way contract with Boston last summer, had 4 points and 4 rebounds in just 6 minutes in Boston’s preseason romp over the Hornets Sunday.

He said he is still adjusting to being pushed around by older, stronger players, and he does not expect many calls to go his way this season. But whenever he is with the main club, he will soak up as much as he can.

“Just got to play a role,” he said, “and learn from the guys that are in front of you.”

Robert Williams progressing with treatment

Mazzulla said that center Robert Williams, who is expected to be out for about 6-10 more weeks after undergoing a maintenance surgery on his left knee last month, is “progressing.” Williams shot free throws on Tuesday and has been attending the team’s film sessions.

“He knows the treatment room is his basketball court right now,” Mazzulla said. “So he’s doing a great job of getting treatment and kind of building towards that.”

Backup center Luke Kornet remains day-to-day with a sprained ankle, but Mazzulla said he’s feeling better.

Getting the veterans ramped up

The Celtics face the Raptors in a preseason game at TD Garden on Wednesday. They will then play the Hornets in Greensboro, N.C., on Friday before closing the exhibition season with an Oct. 14 game against the Raptors in Montreal. Mazzulla said he is still determining how to use his veterans over the rest of the preseason.

“We’ll probably give them a night off at some point, but definitely want to ramp them up also,” he said. “We don’t want to go into a regular season game without them seeing what their strengths are and how we want to play. We just haven’t figured out when that is yet. But we definitely want to see that.”

Alex Barlow named coach of Celtics’ G League team

Alex Barlow on Tuesday was officially named head coach of the Celtics’ G League affiliate in Maine. Barlow played point guard for Celtics president of basketball operations Brad Stevens at Butler and has been part of Boston’s organization since 2015.

“He’s been around here a lot longer than I have,” Mazzulla said. “I’ve learned a lot from him in my time here, and I think he’s a very smart coach. I think he’ll do a great job.”

Former Maine coach Jarell Christian was promoted to general manager.