25-year-old Lux suffered the devastating setback when his knee buckled while running the bases in the Dodgers' spring training matchup against the San Diego Padres on Monday ... closing the curtain on his 2023 campaign.

Lux was visibly upset while discussing the injury with the media just minutes ago ... fighting back tears as he spoke about it.

"You put in a lot of time and work and you really enjoy the guys in the clubhouse," Lux said at the Dodgers' facility. "The hardest part is just not being able to be on the field, for sure."

Lux says he felt his knee pop right away ... and the outside of his leg went numb.

"S*** happens, so control what you can control and crush my rehab and try to be ready for 2024 when it rolls around and that's kinda all you can do," he added.

It was slated to be a big year for Lux, who was going to be the Dodgers' starting shortstop -- a role he's wanted since he was a kid.

"I think every baseball player's dream is to play shortstop for the Los Angeles Dodgers. So, yeah, I think that's one of the hardest parts."

Lux said his teammates have been nothing but supportive throughout the process ... adding it just goes to show "how good these guys in the clubhouse are."

Lux will have surgery next week ... and is expected to be out 8 months.