Celtics guard Marcus Smart grabs his leg after being injured Saturday night against the Los Angeles Lakers. Michael Dwyer/Associated Press

Boston Celtics guard Marcus Smart suffered a strained calf early in the fourth quarter of Saturday’s 96-95 loss to the Los Angeles Lakers, and the team said in a statement Sunday that he’s expected to miss 2-3 weeks.

Smart had an MRI on Sunday morning, and his injury was diagnosed as a tear of his left medial gastrocnemius.

He was hurt when Montrezl Harrell of the Lakers landed on Smart’s foot after leaping for a tip-in. Smart hobbled to the locker room and did not return.

The Celtics have been struggling defensively and are shorthanded in the backcourt, so losing Smart, who is their best one-on-one defender, isn’t ideal. They’ve already been playing without rookie point guard Payton Pritchard, who is recovering from a right MCL sprain, as well as Romeo Langford, who is a long way from returning from a wrist injury. They’re also being cautious with Kemba Walker as he comes back from a knee injury, so he isn’t playing on back-to-back nights.

Smart is averaging 13.1 points and a team-high 6.1 assists.

WALKER HAS stayed remarkably on message since returning to the Celtics’ lineup.

He knew there were going to be ups and downs as he got back into rhythm after missing the beginning of the season rehabbing his knee. The four-time All-Star said he accepted that it was going to take time before he felt and played like he’s used to playing.

But after missing 11 of 12 shots Saturday, including what could have been the winner with 2.7 seconds, Walker was definitely more frustrated than he’s been and admitted as much.

“I would have loved to make some shots tonight. It was a struggle obviously. I would have loved to help my teammates more tonight, but it didn’t go that way. I have to keep working, just find myself a little bit, find my rhythm, find my spots,” Walker said. “It’s more mental than anything I think. I got frustrated at myself and it kind of put myself in a bad place. I’m not even a player like that to really get frustrated. I’m more smiling and I wasn’t that tonight. I got into my own head and mentally I hurt myself and I can’t do that for this team.”

Coach Brad Stevens wasn’t nearly as tough on Walker.

“Kemba has such a wonderful way about him. He’s the greatest teammate. He puts a lot of pressure on himself to be really good. And I think tonight, they put a lot of attention on him, they had a huge presence on him, and it just wasn’t his night,” Stevens said.

“We’re riding Kemba. He is a really good player who really cares about his team and really wants to be a part of something special with guys that are going to give for each other. And sometimes it’s not your night. But more often than not, it is his night. And we believe strongly in that.”

Jayson Tatum shared his coach’s confidence in Walker.

“We just need to look for him more. Get him more involved. Coming back from rehabbing and being on a minutes restriction, it’s tough just trying to find your rhythm,” Tatum said. “We just need to do a better job of getting him involved. He’s one of the best players in this league. Once he finds his rhythm we’re going to be clicking on all cylinders.”

Walker pledged to shake it off.

“I’m a little disappointed in myself personally. But I’ve been around for a minute now. This ain’t the first time I’ve shot the ball bad,” Walker said. “I’ve just gotta look past it. I have no choice, man.”