The Athletics outrighted Rios (shoulder) to Triple-A Las Vegas on Wednesday.
Rios surrendered seven earned runs in 1.2 innings of relief this year with the A's before being diagnosed with Raynaud's syndrome in June. He subsequently underwent surgery in mid-July to repair an axillary branch aneurysm in his right shoulder. The 30-year-old owns a career 6.32 ERA in 92 major-league appearances and is no longer part of the 40-man roster in Oakland.