Panda sightings, which have been few and far between during this young Red Sox season, are about to get even more scarce.

The club on Wednesday placed struggling third baseman Pablo Sandoval on the 15-day disabled list with what manager John Farrell described as a left shoulder strain.

Speaking in the dugout while his teammates took batting practice, Sandoval was in good spirits despite the ailment, which he couldn’t trace to any specific event.

“I wake up this morning with soreness [and] I didn’t have a lot of [range of] motion, so something happened, so [I said], later I will have the doctor look at it when I get here,’’ said Sandoval. “Yesterday I don’t feel nothing like weird. But when I woke up this morning I couldn’t even move my arm. That’s why I was worried about it.’’

Sandoval had “exactly the same’’ feeling a few seasons back but couldn’t recall what the medical diagnosis was.

“I had this before back in 2011, swinging the bat during the game, but I don’t know what happened right now,’’ he said. “Back then it was in the labrum, a spot on the shoulder, but I don’t know what it’s going to be right now. Just waiting for the doctors.’’

It’s the latest setback for Sandoval, 29, who has had a tumultuous start to the season. He lost his starting job during a spring training battle with Travis Shaw and has seen only spot duty, going hitless in six at-bats.

Additionally, video of Sandoval’s belt snapping during an at-bat against the Blue Jays over the weekend went viral, and he also heard scattered boos during Monday’s Opening Day introductions at Fenway Park.

He said he wasn’t “bothered at all’’ by the cold greeting. “I just laughed,’’ he said.

Farrell, who said he first learned of the injury when Sandoval reported for duty Wednesday, thinks he may have tweaked the shoulder doing extra work as he tried to keep sharp in anticipation of an opportunity to get back on the field.

“He’s been hitting a lot extra, before [batting practice] and during the game in the cage,’’ said the manager. “He’s got very limited range of motion. That was revealed after he went through a battery of tests with the medical staff.’’

Farrell acknowledged it’s been a struggle out of the gate for Sandoval and that the stint on the DL could have an extra benefit, as the third baseman can use the time to work on some conditioning.

“It’s been a real tough start. He’s been an easy target,’’ said Farrell. “I’ve had a chance to sit and talk with him about that specifically. First and foremost, we’ve got to get him right physically to get past the shoulder issue. If a breather gives him a chance to maybe step away from the scrutiny that he’s under, we’ll make every effort to have that take place.

“But I still firmly believe that Panda is going to be a contributor to this team. We’re going to need him to be, because there’s a darn good player in there. We’ve got to continue to work to get that out.’’

For his part, Sandoval, now in the second season of a five-year, $95 million contract, said he’s remained positive despite the early adversity. He also said he has “great communication’’ with Farrell.

“I’m not frustrated,’’ he said. “I just want to get healthy, see what the results is today when the doctor sees it. I just want to keep happy. Be happy. Keep my head up. Keep working until I can be back.’’

Pressed further if the opening of the 2016 campaign has him down in the dumps, Sandoval, wearing his ever-present smile, chuckled.

“Why [am I] going to be sad? To be mad? Gimme one reason,’’ he said as his smile seemingly got broader. “I’m alive. I have daughters. One son coming. I have nothing to worry about.’’

Sandoval made it clear that he has no plans on spending this summer — and the foreseeable future — in any place but Boston.

“I sign here for five years, so I’m here,’’ he said with a laugh, when asked if he still believed his future was in a Red Sox uniform. “I’m going be here a lot of years. I love my teammates and the fan support. Where am I gonna go?’’

He reiterated that his focus is on getting healthy and back on the field, and not being a distraction off it.

“There’s gonna be tough moments but the way that I handle all these things, I’m gonna be professional, I’m gonna respect my teammates, respect the fan support, [and the] organization,’’ he said.

“So I’m just going to keep [focused] and working hard and be part of this team for a long time.’’

Farrell said the team and the player are on the same page.

“He has my full support,’’ Farrell said. “Every player has needs. Panda’s are outlined. There’s a specific plan to address those. And we’ll support him through it.’’

To fill Sandoval’s spot, the Sox summoned Josh Rutledge from Triple A Pawtucket. The 26-year-old provides versatility as he can play all four infield positions.

To make room for Rutledge on the 40-man roster, the club shifted righthander Brandon Workman from the 15-day to the 60-day disabled list as he continues to recuperate from Tommy John surgery.

Jim McBride can be reached at james.mcbride@globe.com.