SAN DIEGO -- Jake Arrieta's tenure in San Diego proved to be short-lived.

The Padres designated Arrieta for assignment on Tuesday, when they reinstated righty reliever Javy Guerra from the 60-day injured list. Arrieta had exited his start on Sunday in St. Louis with a right adductor strain that was believed to be minor.

Signed in mid-August amid a spate of injuries to the Padres pitching staff, Arrieta couldn’t deliver the rotation boost that San Diego was desperate for. He mostly struggled in four starts, posting a 10.95 ERA.

Released by the Cubs in mid-August, Arrieta saw the same issues resurface with the Padres. His 91.4 mph average fastball velocity is a career low, and his slider, once a putaway pitch, remained all too hittable. The 35-year-old righty owns a 7.39 ERA across 24 starts this season -- the highest single-season mark for a pitcher with as many starts since the Tigers’ Mike Moore in 1995.

Those struggles seemingly prompt the question of what's next for Arrieta, the 2015 National League Cy Young Award winner and a member of the ‘16 World Series champion Cubs. Arrieta owns a 3.98 ERA and 115 wins across parts of 12 big league seasons. But per Baseball-Reference, he hasn't been worth 1 WAR in a season since 2018.

As for the Padres' beleaguered pitching staff, those injury concerns still haven't resolved themselves. Blake Snell (left adductor strain) and Chris Paddack (right elbow inflammation) are questionable to return this season. Dinelson Lamet, meanwhile, has transitioned to a bullpen role after spending four stints on the IL with elbow trouble. On top of that, Ryan Weathers has struggled, MacKenzie Gore hasn’t broken through, and Adrian Morejon was lost for the year to Tommy John surgery in April.

As the Padres fight for a Wild Card spot, only Joe Musgrove and Yu Darvish remain active from a rotation that was viewed as one of the best in baseball at the start of the season. (And Darvish has battled back and hip trouble during the second half.) The Padres signed right-hander Vince Velasquez to a Minors deal last week after he’d been released by the Phillies, and Velasquez is slated to start against the Giants on Wednesday night.

At the very least, Guerra’s return should provide a boost for the bullpen. The hard-throwing right-hander had missed the entire season with a right UCL sprain. He pitched three scoreless, hitless rehab innings in the Minors before Tuesday’s callup.