Daniel Theis boosts the Chicago Bulls defense again in a 102-96 win over the Boston Celtics. But can they afford to keep the impending free agent?

Coach Billy Donovan made a couple of tweaks to the Chicago Bulls starting lineup over the weekend to make up for the absence of guard Zach LaVine. Not only did he reorganize his backcourt by starting Coby White next to Garrett Temple, but he also made a change in the frontcourt.

Daniel Theis was elevated to the first unit alongside Nikola Vučević, inserting the Bulls’ best rim protector into the lineup to boost their defense. It has paid off so far, with the Bulls giving up just 96 points in back-to-back victories, including a 102-96 win Monday night against Theis’ former team, the Boston Celtics.

The Bulls also surrendered 96 points Saturday to the Cleveland Cavaliers, their lowest opponent total since the trade deadline. It’s only the second and third time in 14 games since the deadline that they held a team to fewer than 100 points.

“We want to be a physical defensive team,” Theis said after shootaround Monday afternoon. “We can’t get into shootouts with teams every night. We want to have a defensive presence, play physical, make it tough for every team, especially when we play with two bigs. We’re tall. We’re physical and make it tough in the paint.”

Theis finished with six points, six rebounds, four assists and one blocked shot, while Vučević led the Bulls with 29 points and nine boards.

Theis was facing his former team for the first time since the Bulls acquired him in a three-team trade with the Washington Wizards at the deadline. He admitted Monday that the trade caught him off guard at the time.

The Celtics reportedly parted with him to remain under the luxury tax given his impending free agency, and the Bulls were able to take advantage.

“He was a big reason why we were defensively ranked where we were,” Celtics coach Brad Stevens said before the game. “Our defense has gotten better here, but we’re still learning to communicate as well as he did and direct as well as he does.

“He’s a guy that we miss, but I’m happy for him. He’s playing really well there. He’s a very versatile player who cares about winning, so he’s a guy that you want on your team.”

In his first 11 games since joining the Bulls, Theis averaged 9.5 points, 4.6 rebounds and 1.9 assists while shooting an impressive 69% on 2-point attempts. His game is an ideal complement to Vučević, pairing a versatile defender with the ability to shoot, pass and protect the paint next to the more offensively minded All-Star.

It’s clear the Bulls are impressed with Theis so far. Donovan said over the weekend the organization is open to the idea of keeping Theis, who will become an unrestricted free agent at season’s end.

“I would say there’s no question that myself and Artūras (Karnišovas) and Marc (Eversley) really like him as a player,” Donovan said. “I would think that our hope would be a long-term possibility.

“With free agency coming up and guys having the opportunity to make their own decisions, I understand that. But he’s someone we really like a lot and feel like could be really good for us going forward.”

The reality of the situation might be more complicated.

Judging by the state of the Bulls, who had lost five of their last six and 13 of 18 entering Monday, they have a lot of work to do in the offseason to get into playoff contention and likely won’t have a first-round draft pick.

Theis, who turned 29 this month, is in the final season of a two-year, $10 million contract. If he’s available at that price, the Bulls potentially could bring him back, but he might be due for a raise on the open market. The Bulls will have to get creative to find ways to improve the roster in the offseason, but they do hold Theis’ Bird rights, which would allow them to exceed the salary cap to re-sign him.

If the Bulls need to clear cap room for a larger addition in the offseason, however, they could renounce Theis’ $9.5 million cap hold.

The Celtics’ salary-cap situation, not Theis’ performance, seemed to be the only reason they traded him at the deadline. The Bulls might find themselves in a similar scenario in the offseason, but finding a way to keep Theis could be added to the growing offseason to-do list.

“Obviously it’s nice to hear that Coach is talking well about me,” Theis said. “I’m just trying to be a veteran guy on this team, help the young guys and listen. I’ve been around basketball for a long, long time. I think I bring a physicality to the team, especially on the defensive end, and I want to bring it every night.”