MESA, Ariz. -- Seiya Suzuki was hoping to help Japan regain its previous World Baseball Classic glory later this spring. But now, the Cubs outfielder is turning his focus to getting back to full strength for the start of his sophomore season in Chicago.

Suzuki informed Team Japan on Monday night that he was withdrawing from the WBC due to a left oblique injury. It was a difficult decision for Suzuki, who has been diagnosed with a moderate strain and is facing the possibility of not being ready in time for Opening Day.

“I know a lot of people were kind of excited to see me out there playing,” Suzuki said on Tuesday morning via interpreter Toy Matsushita. “So it's just a really unfortunate decision. It's just very unfortunate.”

Suzuki was scratched from his scheduled start in the Cubs' Cactus League opener on Saturday due to tightness in his left side. He underwent imaging on Sunday, and the team's medical staff went over the results on Monday. Suzuki said he was “shocked” to learn of the setback’s severity.

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“I'm sad for him that he doesn't get to represent his country,” Cubs manager David Ross said. “I know that was important for him. Things happen and injuries pop up. I think the good news, if I was going to be positive, is that it's right now when things don't matter, and we've got time.”

While the Cubs did not announce a timetable for Suzuki’s return, Ross acknowledged that oblique injuries can be “pretty tricky” for players. The rehab and build-up process could take weeks, making a return in time for Chicago’s March 30 season opener against the Brewers an optimistic scenario.

Ross said the team would not treat Opening Day as an “artificial deadline."

“The goal for us,” Ross said, “is when he's back, we don't lose him again. So, pushing it towards some date that we all look forward to doesn't make a whole lot of sense. We want him to get back completely healthy. And if that's Opening Day, great. If it's five days in, great. If it's two weeks in, fine, you know?

“We'll be sure and communicate throughout this process, and get him back when we won't have to worry about it throughout the season.”

Over the offseason in Japan, Suzuki worked to add muscle with the goal of improving his "physicality" -- as he explained via Matsushita earlier in camp -- and stamina for the upcoming season. Listed at 182 pounds in the Cubs' 2022 media guide, Suzuki said he reported this spring 20 pounds heavier.

"The strength and the size is noticeable," Cubs hitting coach Dustin Kelly said. "The swing hasn't changed much, which is a good thing. He has one of the most mechanically sound swings in this game. And with the added strength and bulk, it didn't compromise that at all. So we're excited about it."

Suzuki had been backing that excitement up with powerful displays in early spring batting practice, adding to the Cubs' hope that he could be on the cusp of a big season. After signing a five-year, $85 million contract last year, Suzuki hit .262/.336/.433 with 14 homers, 22 doubles and 46 RBIs in 111 games in his rookie season.

Ross said there was no way to say whether Suzuki’s bulkier physique was to blame for the setback.

“We could be saying the same thing if he didn't put on weight,” Ross said. “I think the goal was to identify where he wanted to get better. He did that. He came in looking really good. The ball was coming off his bat really well.”

It was a season of adjustments for Suzuki, who not only had to adapt to Major League pitching, but to a new city and country. He got off to a strong start (taking home the National League Rookie of the Month honor for April), then dealt with an injury and some hitting woes in the middle of the season before finishing strong (.906 OPS in his final 32 games).

“[I wanted to] make sure I don't drop my weight too much,” Suzuki said. “With all the travel, it does have a toll on your body. So I wanted to be 100% in terms of my body, and that's what I did during the offseason just to make my body a little stronger."

The 28-year-old Suzuki had the Cubs' support when it came to participating in the WBC. At the start of Spring Training, Suzuki spoke about the chance to play alongside Yu Darvish and Shohei Ohtani, with the goal of winning the tournament like Japan did in 2006 and '09.

“I'm going to watch them and just cheer them on,” Suzuki said.