Alvarez, 25, spent the past three seasons with the Marlins. Over his five-year career, which also includes two seasons with the Blue Jays, he is 27-34 with a 3.80 ERA.
After an All-Star campaign in 2014, Alvarez went 0-4 in 2015 with a 6.45 ERA in four games (all starts). He was the Marlins' Opening Day starter but underwent arthroscopic surgery in August to repair a right shoulder injury that had sidelined him for much of the season.
To clear a spot on the 40-man roster, the A's designated right-hander Arnold Leon for assignment. Leon, 27, made his Major League debut last season and was 0-2 with a 4.39 ERA in 19 games.
Fantasy spin | Fred Zinkie (@FredZinkieMLB)
Alvarez will likely go undrafted in most 2016 mixed leagues after missing most of last season with a shoulder injury that required surgery. But if he proves to be at full strength early in the season, he will be a popular waiver-wire acquisition. After all, the right-hander posted a 3.23 ERA and a 1.23 WHIP across 51 starts as a member of the Marlins from '13-15. However, his lack of strikeout stuff -- as evidenced by a 5.1 K/9 rate in the aforementioned stretch -- will limit his regular usage to deep mixed leagues. Those in shallow formats should use Alvarez as a spot starter and instead seek full-time rotation members with the potential to produce both low ratios and high strikeout totals.
Joey Nowak is a reporter for MLB.com. Follow him on Twitter at @joeynowak. This story was not subject to the approval of Major League Baseball or its clubs.