General manager David Stearns says he hopes to have Miley in big league camp on Friday.
Miley, 31, went 8-15 with a 5.61 ERA in 32 starts for the Baltimore Orioles last season. He had a league-high 93 walks.
Miley also had 142 strikeouts over 157⅓ innings, making him an attractive candidate for a team looking to add pitching depth.
Miley won 16 games and was an All-Star as a rookie for Arizona in 2012. He is 66-74 with a 4.38 ERA in 200 appearances in his career, including 196 starts.
"Clearly, the last two years haven't been as successful, but we have some ideas why and he has some ideas why," Stearns said Thursday. "He's coming into camp to compete, he's coming in to see if he can earn a spot here, and if he can, that's great."