The Minnesota Twins put Bailey Ober on the 15-day injured list before Sunday’s game because of right elbow inflammation, and he is scheduled for an MRI on Monday. The move leaves Minnesota with only four healthy starting pitchers at a time when the rotation was already under strain.

That matters now because the Twins are trying to hold together a staff that has been hit in quick succession. Earlier in the week, they placed Kendry Rojas on the injured list with left elbow inflammation, and on Saturday they designated Simeon Woods Richardson for assignment. The only other healthy starting pitchers are Joe Ryan, Connor Prielipp and Taj Bradley, while two of the club’s healthy starters are having their workloads actively managed.

The roster crunch landed on the same day the Twins were beaten 9-3 by the Pittsburgh Pirates at PNC Park, a loss that completed a series sweep and left Minnesota at 27-33. Zebby Matthews was tagged for seven earned runs in the defeat, and the Twins finished the trip having lost six of 10 games and five straight overall.

The bigger concern for Minnesota is not just who is hurt, but how the pitching has unraveled over the past 10 games. Since arriving in Boston on May 22, Twins starters have posted an 8.31 ERA with 44 earned runs allowed in 47 2/3 innings, a sharp fall from the eighth-best starting rotation ERA in the majors when the trip began at 3.67. That collapse has turned a stretch that should have steadied the club into a daily search for innings.

Matthews said he got results when he executed pitches, but added that the Pirates punished the mistakes he left over the plate. That was the shape of the weekend for Minnesota as Pittsburgh hit well throughout the series, and it is the same problem now facing the Twins’ front office and staff: the depth chart is thinning faster than the schedule is easing.

With seven consecutive games coming against the Chicago White Sox and Kansas City Royals, the next move may not come quickly. When asked who would take Ober’s place, Derek Shelton said it was “five days from now,” then added that the club would try to get through Sunday night and Monday before deciding as a group how to proceed. For the Twins, the issue is no longer whether the rotation is stretched. It is how long they can keep it functioning at all.