Brennan was selected by the Mariners with the 13th pick in the Rule 5 draft.
Brennan was signed to a minor-league contract by the Rockies this offseason, so he is an unusual selection in the Rule 5 draft. He never pitched for the Rockies, most recently logging a 3.25 ERA, 1.08 WHIP and 79 strikeouts in 74.2 innings in the White Sox's system, primarily at Double-A. Those are impressive numbers, but considering he is already 27 years old, they don't carry much weight. If he sticks with Seattle, he will likely be used as a spot starter or long reliever.