The Cubs sent rookie pitcher Caleb Kilian back to the minor leagues Tuesday, optioning the right-hander to Triple-A Iowa.

Kilian, 25, allowed 7 runs (5 earned) in 2.1 innings against the Pirates in Pittsburgh Monday, walking 5 batters and allowing 3 hits.

He has a 10.32 ERA in 3 MLB starts with 12 walks in 11.2 innings.

“We just talked bout being aggressive and finding what he does well,” David Ross said in an interview with Taylor McGregor Tuesday. “Getting back to pounding the zone, not thinking about the edges or spinning the breaking ball in fastball counts.

“It looked like things were moving a little bit fast and he couldn’t get the command of the baseball. His strength is that 2-seam fastball. It looked like he wasn’t able to command that yesterday.

“[We talked about how] hitting’s really hard, making these guys barrel up the baseball. When you fall behind, you put yourself in a box. The hitter’s able to zone things in and it makes it really difficult to have success.”

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Kilian is the Cubs’ top pitching prospect. The team originally called him up to provide rotation depth during a doubleheader for his MLB debut on June 4.

As the Cubs’ starting staff has been hit hard by injuries, Kilian was recalled and inserted into the rotation, making a start on June 15 before Monday’s outing.

Walks have not been an issue for Kilian in the minors this season, as he has been lights out in Triple-A. He is 2-0 with a 2.51 ERA in 10 starts for Iowa, with 47 strikeouts and only 16 walks in 43 innings.

The Cubs hope Kilian will head down to Iowa with a clear plan as he continues his development.

“Being aggressive early in the zone throwing strikes is a simple message,” Ross said. “Just kinda hitting the reset button for him and getting something simple to think about in his work moving forward and going out and working towards that next start.”

To take Kilian’s spot on the roster, the Cubs recalled pitcher Mark Leiter Jr.

Leiter, 31, has pitched in 7 games (3 starts) for the Cubs this season, posting a 6.23 ERA and 1.39 WHIP in 17.1 innings.