Ahead of the third game of their series against the Rockies, the Cubs announced a plethora of roster moves. The Cubs selected the contracts of Mark Leiter Jr., who will start Saturday night’s game and Locke St. John, who was optioned to Iowa.

Alfonso Rivas was optioned to Iowa to make room on the 28-man roster in Chicago. To clear room on the 40-man roster for Leiter Jr. and St. John, right-handed pitcher Cory Abbott outfielder Greg Deichmann were designated for assignment.

Leiter Jr. impressed in Spring Training for the Cubs and was one of the final cuts of the spring, posting an 0.93 ERA and a 1.24 WHIP in 9.1 innings of work. Leiter made one start at Triple-A Iowa this month, striking out 7 and allowing 1 earned run in 4 innings on April 8 against Buffalo.

“We’ll bring him in here and give him a chance to see what he’s capable of,” Ross said prior to Friday night’s loss in Colorado. “Had a really nice spring for us. Throws strikes. I love his splitfinger, it’s real. A lot of good qualities.”

He’s made 47 appearances in the big leagues across 2 seasons, including 11 starts in 2017 with the Phillies. He last appeared in the majors in 2018 with the Blue Jays. That experience is crucial, too.

“When you watch some of the young guys go out, you just wanna make sure the adrenaline, the emotions are kept under control. You have a little less of that with the guy that’s had some big-league time,” Ross said. “We call it that third deck league and that definitely jumps on a lot of guys. Jumped on me when I first got up. I think everybody has a little bit of — you add that top tier level in the stadiums and it makes a big difference.”

Leiter Jr. provides immediate cover in the Cubs starting rotation.

The Cubs have four starters on their active roster — Kyle Hendricks, Justin Steele, Marcus Stroman and Drew Smyly — with Keegan Thompson pitching in long relief in his two appearances. After Thompson completes his two-game suspension Saturday, having both he and Leiter Jr. offers some options for Ross.

They could elect to start one or the other in the rotation while Wade Miley (elbow inflammation) and Alec Mills (back) continue to return from their injuries. They also provide depth to the starting rotation who are still on pitch restrictions — Hendricks is the only starter to have thrown more than 80 pitches, when he threw 83 on Opening Day. Ross could elect to piggyback Leiter Jr. or Thompson off a short start and bridge the gap to his bullpen.

St. John’s addition to the 40-man roster provides another lefty option on the roster for the Cubs. The Cubs have just three lefty arms on their active roster, starters Steele and Smyly and reliever Daniel Norris. The Cubs could choose to bring up St. John if they feel a need for another lefty pitcher. He’s made 3 appearances at Iowa this season — all in relief — striking out 4 and allowing 3 earned runs in 4.1 innings of work.

Rivas has 2 hits in 4 at-bats this season. He’s started two games this season.

“First thing I say when those happens is this sucks, for all of us,” Ross said Saturday. “It’s just part of the options game when you’ve gotta make a move for a pitcher. Those things happen throughout a season, it’s never good news.