CHICAGO - The Pittsburgh Pirates can't seem to avoid injuries and this one has hit their bullpen.
The Pirates placed right-handed pitcher Isaac Mattson on the 15-day injured list with right hip impingement ahead of the series opener vs. the Chicago White Sox at Rate Field on Sept. 8, but retroactive to Sept. 6.
Pittsburgh recalled left-handed relief pitcher Brandon Eisert from Triple-A Indianapolis, who will take Mattson's place in the bullpen.
It's the second injury in the Pirates' bullpen in a week, as right-handed pitcher Kirby Yates is on the 15-day injured list with right shoulder impingement.
There weren't many better pitchers in the Pirates' bullpen in 2025 than Mattson, who found what he needed and succeeded in his first long MLB stint.
Mattson hasn't followed up on that form this season, posting a 5.35 ERA over 38 games and 38.2 innings pitched, 36 strikeouts to 18 walks, a .282 batting average allowed (BAA) and a 1.60 WHIP.
Aug 17, 2026; Pittsburgh, Pennsylvania, USA; Pittsburgh Pirates relief pitcher Isaac Mattson (72) pitches against the Detroit Tigers during the fourth inning at PNC Park. Mandatory Credit: Charles LeClaire-Imagn Images | IMAGN IMAGES via Reuters Connect
He has bounced between Pittsburgh and Indianapolis five times, doing so three times since Aug. 1.
Mattson had a strong start to 2026, a 1.13 ERA through his first 13 appearances, but after giving up five runs against the St. Louis Cardinals at PNC Park on April 30, a 10-5 loss, he's been far less effective, with an 8.34 ERA over his last 22 outings.
He's struggled in many different areas , with opposing hitters posting a high hard-hit rate (52.1%) and barrel rate (12.4%), which would rank him among the worst pitchers in baseball if he were qualified.
His last outing vs. the Los Angeles Angels at PNC Park on Sept. 5 also didn't go well, giving up three runs in his second inning of work in the 6-1 defeat.
Mattson can come off the injured list on Sept. 21, so he could return for the final two series of the season.
The Pirates have 10 pitchers in their bullpen, with one fewer starter due to Mitch Keller 's season-ending injury and an extra arm with the expanded rosters in September.
Pittsburgh has seven right-handed pitchers in Lake Bachar , Khristian Curtis, Wilber Dotel, Camilo Doval , Carmen Mlodzinski , Yohan Ramrez and Luke Weaver , plus left-handed pitchers in Eisert, Mason Montgomery and Gregory Soto .
Bachar will likely start the bullpen game, scheduled for the next contest vs. the White Sox on Sept. 9, and Curtis, Dotel, Mlodzinski, plus Ramrez are all middle-relief options after him.
Doval and Weaver, plus Eisert and Soto, can all throw an inning if called upon and Montgomery has been excellent in the closer role .
The Pirates need a big series from their bullpen, as they try and make a late run at the postseason .
This article was originally published on www.si.com/mlb/pirates/onsi as Pirates Place Relief Pitcher on Injured List Before White Sox Game .
