Sonnanstine, 29, had appeared in four Cactus League games, giving up eight runs on 13 hits and three walks over five innings. He struck out three. Last season, the right-hander was 0-2 with a 5.55 ERA in 15 games (four starts) with the Rays.
With the move, Sonnanstine was taken off the Cubs' 40-man roster, which is now at 39. The spring camp roster is 47 and consists of of 21 pitchers (five non-roster invitees), five catchers (two non-roster invitees), 12 infielders (five non-roster invitees) and nine outfielders (three non-roster invitees).