The Mariners have released righty Justin De Fratus, the team announced (via Ryan Divish of the Seattle Times, on Twitter). The out-of-options reliever had signed on to a major league deal worth a reported $750K, though it’s certainly possible that not all of that was guaranteed if he didn’t break camp with the club.

De Fratus had thrown six frames this spring, allowing four earned runs on six hits and three walks while striking out four. Divish notes that he was working in the 89 to 90 mph range, and obviously wasn’t showing what Seattle hoped to see when it gave him a 40-man spot.

The news constitutes the latest setback for De Fratus, who had a nice 2014 season in which he threw 52 2/3 innings of 2.39 ERA ball with 8.4 K/9 against 2.1 BB/9. But last year was a letdown, and he found himself outrighted by the Phillies after working to a 5.51 ERA over 80 innings.

Seattle’s rebuilt bullpen is showing some cracks this spring, as potential options such as Ryan Cook, Charlie Furbush, and Evan Scribner are all dealing with injury issues. As MLB.com’s Greg Johns notes on Twitter, the M’s could be looking to add pen depth over the coming weeks.