When a player's contract is designated for assignment -- often abbreviated "DFA" -- that player is immediately removed from his club's 40-man roster, and 25-man roster if he was on that as well. Within seven days of the transaction (it was previously 10 days), the player must either be traded, released or placed on irrevocable outright waivers.
Gallardo, 32, is a 12-year veteran who had his best years with the Brewers and was a National League All-Star in 2010. He was 13-11 with a 3.42 ERA in 33 starts for the Rangers in 2015 and 5-10 with a 5.72 ERA in 22 starts and six relief appearances for the Mariners last season.
"Obviously we have first-hand experience with him, and we had interest in bringing him back this offseason after how he threw the ball late last season," Rangers assistant general manager Josh Boyd said. "He competes. We'll get him built up to provide us with veteran starting pitching depth."
The Rangers' starting depth has been hit hard by injuries. Clayton Blackburn and Ronald Herrera were supposed to be in Round Rock's starting rotation but began the season on the disabled list.
The Rangers are also without Doug Fister at the Major League level. He is sidelined at least two weeks because of a strained right hip muscle.