Adrian Gonzalez sits out for Dodgers

Reporting from PITTSBURGH —  In the midst of a horrific slump, Dodgers first baseman Adrian Gonzalez received a pair of days off to finish this series in Pittsburgh. Manager Dave Roberts suggested Gonzalez required a “mental blow,” and will be ready to play again on Tuesday in Milwaukee.

“You look at over the last couple weeks, not swinging well,” Roberts said. “I think sometimes it’s good to get away.”

Roberts intended to rest Gonzalez for Monday’s matinee against Pirates left-hander Francisco Liriano. He sat Gonzalez for Sunday’s game against right-handed rookie Chad Kuhl after Gonzalez went 0 for 4 the day before.

Based on the metric of on-base-plus-slugging percentage, this has been the worst month of Gonzalez’s career. Gonzalez has posted a .513 OPS this month. His previous nadir was a .575 OPS in June of 2014. Gonzalez appears stuck in a cycle of rolling grounders to the right side and hitting soft flyballs to the left.

Gonzalez has dealt with injuries to his neck and back this season. Roberts insisted those have not caused his decline.

“I’m of complete certainty that it isn’t [a physical issue],” Roberts said. “And even talking to the training staff, [they say] it ‘s not physical. He feels great.”

No starter decided for Wednesday

The Dodgers have yet to determine who will start on Wednesday in Milwaukee. Forced to use Nick Tepesch in an emergency on Friday, the team will once again dip into its minor league depth. The list of candidates is small. Roberts indicated Hyun-Jin Ryu, Brandon McCarthy and Mike Bolsinger are not being considered.

That leaves a small pool. One potential option is Brock Stewart, a 24-year-old right-hander who started the season with Class-A Rancho Cucamonga. He graduated to double A, where he dominated Texas League hitters. In three starts for triple-A Oklahoma City, Stewart has a 2.89 earned-run average with 27 strikeouts in 18 2/3 innings.

“You look at what we have internally, you look at guys that have performed,” Roberts said. “There’s a lot of things that should be on the table. Certainly Brock’s performed up to this point.”

Andy.mccullough@latimes.com

Twitter: @McCulloughTimes