Munoz unexpectedly flew home to the Dominican Republic, causing the team to question whether he would return, Cardinals president of baseball operations John Mozeliak said, according to Derrick Goold of the St. Louis Post-Dispatch.
"Trying to determine what is the next, best step, we just decided based on what we're hearing from his agent, maybe cutting ties make the most sense," Mozeliak told Goold. "He just wasn't happy here and was frustrated with how he was used last year. Didn't like the writing on the wall that he was seeing this year."
The 25-year-old was competing for a big-league roster spot with Tommy Edman, Brad Miller, and prospect Edmundo Sosa before he injured his hamstring. He was scheduled for an examination Thursday but never showed.
A teammate then told the club about Munoz's flight home.
"More opportunities were going to come Yairo's way with the extra (spot) on the bench," Cardinals manager Mike Shildt said. "He was going to see more opportunities. I wish him the best. I wish I had a better explanation. It's been baffling."
The Cardinals acquired Munoz from the Oakland Athletics in 2017 as part of a deal for outfielder Stephen Piscotty.
In 196 games over the past two seasons, Munoz slashed .273/.331/.391 with 10 home runs, 23 doubles, and 55 RBIs.