Trout, dealing with left rib cage inflammation, hasn't played since July 12. He was a late scratch from the lineup in the Angels' 7-1 loss to the Los Angeles Dodgers last week before the All-Star break.
Head athletic trainer Mike Frostad told reporters on Saturday that Trout had a cortisone injection in his back on Thursday.
"The injection was done into the joint where the rib meets up with the spine," Frostad said. "So it's kind of a difficult area to get to and he just has to let that cortisone take effect. He's doing some stuff right now that doesn't involve rotation."
Frostad said Trout will be day-to-day as the Angels continue to evaluate the slugger, who said he's been dealing with the issue since the start of the month.
Trout, 30, is slashing .270/.368/.599 with 24 homers this season for an Angels team 11 games out of the wild-card race.