Kristaps Porzingis will miss at least one week after the big man suffered a left calf strain in Friday’s loss to the Magic, Celtics coach Joe Mazzulla said on Sunday.

Porzingis left during the third quarter of Friday’s loss and did not return after he felt some tightness. He did not think the injury was serious, posting on Instagram on Saturday that he received good news after reportedly having an MRI. But the big man will miss several games before the Celtics re-evaluate him.

“I think it’s just a matter of how he feels,” Mazzulla said. “How it kind of heals when people look at it again after a week or so.”

Porzingis will likely miss at least three games – Sunday’s game against the Hawks, Tuesday’s matchup with the Bulls and Friday’s tilt with the 76ers – as he heals his injury. But it’s possible he doesn’t miss more than that thanks to a tweak in the schedule due to the In-Season Tournament. If the Celtics do not qualify for the quarterfinals of the tournament, their next game after Friday wouldn’t come until the following Wednesday as the C’s would get four days off.

Still, there will be a big adjustment without Porzingis, who has fit seamlessly with the Celtics offensively providing a new dimension and defensively as a rim protector. They struggled on the interior in Friday’s loss after Porzingis left the game, as the Magic converted 13 offensive rebounds into 21 second-chance points and scored 60 points in the paint. Al Horford will start in his absence, with Luke Kornet getting some increased playing time off the bench.

“We created an identity last year of playing small with our shift activity and our ball pressure and our individual defense, so regardless of if there’s a five on the perimeter or not, we just have to continue to take pride in our individual defense,” Mazzulla said on what changes without Porzingis. “I think that comes from our shift activity, knowing who you’re guarding, can you help stop the ball and get out to a shooter? …

“it’s going to look different without (Porzingis), but Al and Luke do a great job, we’ve had good defenses with those guys for numerous years now, so it may look a little bit different, and just everyone’s gotta be a little bit better.”

No risk taken

The Celtics are in danger of missing out on the quarterfinals of the In-Season Tournament even if they beat the Bulls in their group play finale on Tuesday. A win would create a tie with the Magic at the top of the group with 3-1 records, but the Magic own the head-to-head tiebreaker. There could be a three-way tie if the Nets beat the Raptors, and the second tiebreaker would go to point differential.

Heading into Tuesday’s game, the Celtics have a point differential of 0, while the Nets are at plus-8 and the Magic finished at plus-22. The C’s would need to blow out the Bulls to have a chance to win the group.

The Celtics lost by 17 in Friday’s loss to the Magic and Mazzulla emptied the bench late in the game. Though the point differential equation was something he was aware of, he decided it wasn’t worth the risk of his starters staying in the game.

“I thought about it but at the end of the day, Jrue (Holiday) was out, we had lost Porzingis. I wasn’t willing to risk a point differential for the sake of the long-term health of our team,” Mazzulla said. “That was kind of the decision that I made there. It’s obviously something that you process and go through.”

Tip-ins

Jrue Holiday missed his second consecutive game Sunday due to the ankle sprain he suffered in Wednesday’s loss to the Bucks. The guard went through warmups prior to Sunday’s game but was later ruled out. … Dalano Banton made his first Celtics start Sunday against the Hawks in Holiday’s absence.