To make room on the 40-man roster, veteran right-hander Logan Kensing was released.
Martin went 2-3 with a 5.40 ERA in 21 games in relief for the Braves last year, then was acquired by Oakland in a July 2 trade. He appeared in four games for the A's, including two starts, going 0-2 with a 14.00 ERA.
Martin, a seventh-round Draft pick by the Braves in 2011, is 31-29 with a 3.24 ERA in 118 Minor League games. He was 1-3 with a 2.10 ERA in seven games (six starts) with Triple-A Gwinnett in the Braves' system and 4-4 with a 5.