Alvarez, 25, had been on the 60-day disabled list all season while recovering from surgery to remove bone chips in his elbow in early April. He had recently begun a rehab assignment and pitched to a 2.25 ERA (1 ER/3.2 IP) in three rehab appearances with Single-A Stockton (two outings) and Triple-A Nashville (one outing). Alvarez went 3-3 with five saves and a 4.11 ERA (16 ER/35.0 IP) in 31 relief outings for Nashville last year, striking out 41 batters in 35.0 innings pitched.
The righthander has spent parts of the last two seasons in the big leagues with San Diego (2014) and Oakland (2015), posting no record and a 7.39 ERA (23 ER/28.0 IP) in 31 career major league outings.
Alvarez was originally selected by the Los Angeles Angels of Anaheim in the third round of the 2012 Draft out of Florida Atlantic University.