The Celtics’ defense was 22nd in the NBA without Marcus Smart. Lucky for them, he’s back

Marcus Smart's intensity has been missed by the Celtics.Jim Davis/Globe Staff

The Celtics have a good core of talented offensive players, but they understand that their defense will ultimately need to lead them. When Marcus Smart, the foundation of this team’s wall, suffered a calf strain during the Jan. 30 loss to the Lakers, the Celtics had the league’s 10th-ranked defense. Since then, Smart has watched helplessly as opposing stars gashed Boston with one dominant performance after another.

In 18 games without Smart, Boston’s defense ranked just 22nd in the NBA.

But reinforcements have arrived. Smart practiced Wednesday and said he plans to play against the Nets Thursday.

“We’re not saying that everybody [needs to] go out there and be Defensive Player of the Year,” Smart said, “but we just want to see everybody go out there and give the effort to give us a chance.”

Coach Brad Stevens said Smart’s playing time will be restricted for at least several games — and Stevens said he had yet to receive official word about Smart’s availability for the Brooklyn game — but Smart on a time limit is better than no Smart at all. He is averaging 13.1 points, 6.1 assists, and 1.8 steals this season, all career highs.

“He’s a good player,” Stevens said. “He’s a guy that knows how to play, plays at both ends of the court, makes us better at both ends of the court, so obviously that’s going to help a ton.”

Marcus Smart works on his rehab before the start of a recent game at the TD Garden while team owner Wyc Grousbeck walks by and greets himJim Davis/Globe Staff

The Celtics are tantalizingly close to having their entire roster healthy and available for the first time this season. Second-year wing Romeo Langford, who has been sidelined all year after undergoing offseason wrist surgery, has been cleared to return, but he was held out of Wednesday’s practice under COVID-19 health and safety protocols.

Stevens said that Langford had been on track to play against the Nets but is now unlikely to make the trip to Brooklyn.

For now, Smart’s presence should provide a considerable boost. In addition to his skills as an All-NBA defender, he is the Celtics’ emotional leader. He can shift a game’s tenor with one startling, sprawling dive across the floor, and he can shift his teammates’ focus level with one fierce rebuke.

He was unable to do any of those things while he was out, and that was difficult.

“I think [it’s hard] for anybody that’s sitting on the sideline because of an injury or something they can’t control to look at,” Smart said, “especially when you know the good defensive team that we can be.”

Wednesday was Smart’s first five-on-five action since his injury, and he said he felt “great” afterward. During the All-Star break, he mostly completed one-on-one basketball workouts and calf-strengthening exercises. Calf strains can aggravate easily, but Smart is confident in his rehab and will not let a potential recurrence take a mental toll.

Marcus Smart is helped off the court late in a January loss to the Lakers.John Tlumacki/Globe Staff

“You have to trust your body, you have to trust the work that you’re doing, and just go out there and do it and just play,” Smart said. “Everything will work itself out.”

The return of Smart and the looming season debut of Langford should be helpful to the Celtics brass as they figure out how to maneuver prior to the March 25 trade deadline.

Regular starters Smart, Jayson Tatum, Jaylen Brown, Kemba Walker, and Daniel Theis have played a total of just 21 minutes together this season. So while flaws were revealed during the bumpy first half of the season, it was impossible to truly evaluate the roster because it simply had not been whole.

“[We have] an opportunity to come out and start fresh with the defense and kind of reinvent ourselves identity-wise on the defensive end,” Smart said. “I just want to see my guys play with the same intensity I have. I’m not saying you have to go out there and play the exact way I do, just the same intensity.”