Harrison, placed on the 15-day disabled list on April 11, likely won't return to the Rangers' rotation until after the All-Star break.
"The surgery went as expected, no surprises," Daniels said. "We don't have any update as far as a timeline, but it's in the ballpark of, give or take, three months."
According to Daniels, the disk herniation was pressing on a nerve in Harrison's back, causing discomfort and weakness in his leg.
Harrison was the Rangers' Opening Day starter after winning 18 games last season, but Daniels isn't panicking.
"You're always thinking about the next pickup," Daniels said. "But we have a couple of guys on the mend, so hopefully we can avoid another hiccup."