Mijares was absent from Monday's first official workout for pitchers and catchers because of an unspecified issue at home in Venezuela. Disappointed manager Ron Gardenhire said Mijares is expected to arrive in Fort Myers on Tuesday or Wednesday.
The Twins didn't learn of the delay until Monday morning.
"He's got to be a little more accountable," Gardenhire said, adding that Mijares would not be fined.
Mijares also missed the team's annual fan festival last month because of a visa problem. The 25-year-old left-hander had a 2.34 ERA in 71 appearances last season. The Twins have been concerned about his conditioning in the past. Their bullpen is crowded, too.
"He knows the days you're supposed to be here. Everybody's here, except one guy. That should tell him a little bit about himself," Gardenhire said. "He's got to figure it out and do a better job. We've got plenty of people who want to pitch."