Alvarez underwent shoulder surgery in July and, after signing a one-year deal with the A's this winter, could be joining their rotation by the end of May.
His addition figures to be a big boost to an A's starting staff that will soon have Alvarez as part of a 1-2 rotation punch with ace Sonny Gray. Oakland starters entered Tuesday with an American League-leading 3.00 ERA, but they're averaging just 5.54 innings per outing.
Alvarez, who turned 26 on Monday, struggled with the Marlins in his four starts that preceded his surgery, but he was excellent for them in a 2014 All-Star season, posting a 2.65 ERA while totaling 187 innings.
Jane Lee is a reporter for MLB.com. Follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.