Skaggs, who received a PRP injection, left Friday night's game against the Rangers with the injury.
"Tyler saw both Dr. Ron Kvitne and Dr. Steve Yoon today for a follow up appointment," the Angels said Monday in a statement. "After his imaging and clinical exam, he was diagnosed with a grade 2 right oblique strain and was administered a PRP injection. These injuries generally include a 10-12 weeks timeline before return to play."
He went on the 10-day disabled list Saturday along with first baseman C.J. Cron, who fouled a ball off the top of his foot in the eighth inning Friday night.
Skaggs, 25, is 1-1 with a 3.99 ERA in five starts this season. He had Tommy John surgery in 2014.
The Angels are already without Garrett Richards, another member of the starting rotation. Richards is on the 60-day disabled list after he was diagnosed with a strained right biceps earlier this month.