Don Mattingly said Monday that he’s committed to keeping struggling veterans Dan Haren and Josh Beckett in the Dodgers’ starting rotation for now. That hasn’t changed since yesterday, when Beckett lost to the Chicago Cubs. The two pitchers are 1-7 with an 8.34 earned-run average since July 1.

What has changed since yesterday is that the Dodgers have a pitcher who’s started 20 games this season in their bullpen.

Carlos Frias, a 24-year-old right-hander, was selected from Triple-A to take the roster spot of Chris Perez after an MRI on Perez’s left ankle revealed bone spurs. Perez was placed on the 15-day disabled list and Paul Maholm was transfered to the 60-day disabled list, officially ending his season.

For now, Mattingly said that Frias will inherit the long-reliever role that Maholm vacated. However, Frias was taking batting practice with the Dodgers’ other starting pitchers Monday afternoon.

Frias will be making his major-league debut with the Dodgers, who signed him out of the Dominican Republic at age 17 in 2007.

Frias was 8-4 with a 5.01 earned-run average, along with 65 strikeouts and 21 walks in 91 ⅔ innings with Triple-A Albuquerque this season. He began this season with Double-A Chattanooga, where he allowed just 12 runs in five starts.

In 2013, Frias made the leap from the low-A Midwest League, to the high-A California League, to Double-A in one season.