CHICAGO — The first true test is looming for the Chicago Cubs in the wake of Shota Imanaga’s injury.

The Cubs will be without their ace for at least two turns through the rotation and this weekend in New York represents the first hurdle for the team.

Imanaga was placed on the 15-day IL Monday and the Cubs have yet to tip their hand for how they plan to replace the southpaw in the rotation.

Thursday’s off-day provides an opportunity to shift around the rotation, but the Cubs don’t want to mess with the rest of the staff.

“Saturday would be the day we’re trying to figure out how we want to play that,” Cubs pitching coach Tommy Hottovy said Wednesday morning.

Jameson Taillon will start the opener against the Mets on Friday in New York and the Cubs could opt to move Matthew Boyd up a day to pitch Saturday on regular rest thanks to the off-day.

But they don’t see a benefit in doing that. No matter what, the Cubs would have to find somebody to fill out the fifth spot in the rotation at some point — or roll with a bullpen day in one of the games.

As of Wednesday afternoon, the Cubs don’t yet have a plan finalized for how they will fill Imanaga’s spot.

“We really want to see how we get through these [games],” Hottovy said. “We’ve got opportunities. We still have Matt Boyd, who we know is going to pitch in the New York series. He’s going to face the Mets, he’s going to face the White Sox [next weekend at Wrigley Field] so moving him a day up doesn’t really benefit us a whole lot. He’s still gonna pitch in those two series.

“Trying to keep him on a good schedule so he doesn’t have to change it and alter his program too much, I think is important. We do have opportunity to move him up, but I think ideally we’d like to kind of keep him on Sunday still and just try to figure out [Saturday].”

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Top pitching prospect Cade Horton remains an option to start on Saturday but the Cubs have also liked the way he has grown and developed in Triple-A after missing most of last season due to injury.

Veteran Chris Flexen was called up last week and has built up to a starter’s workload. But he also pitched an inning out of the bullpen in each Tuesday’s and Wednesday’s game, though manager Craig Counsell confirmed Flexen is still in the mix for Saturday.

If that holds true over the next couple of days, the 30-year-old affords the Cubs myriad options.

They can give Flexen a spot start on Saturday, allowing Horton at least one more start in the minors to continue his development before coming up to debut against the Chicago White Sox next weekend in a softer landing.

Another option is to roll with a bullpen game on Saturday, potentially with an opener and Flexen providing multiple innings in relief. That will be heavily contingent upon how Friday’s game plays out — if the Cubs need their relievers to eat a large chunk of innings in that game, it makes a bullpen game on Saturday tougher to pull off.

Of course, the Cubs could also add Flexen into the rotation for multiple starts and opt to leave Horton in the minors until later this summer.

“He’s been pitching fantastic,” Hottovy said of Horton. “For a guy who battled some ups and downs last year, some mechanical stuff and some struggles to take to the off season that he did and come into spring training ready to work, he’s picked up kind of where we all hoped he would heading into the season.

“He’s gone down and performed at a high level. We’ve challenged him with some things to continue to get better, and he keeps stepping up with in everything we give him. He continues to improve, continues to get better. We’re excited for where he is and what he’s gonna be able to do.”

One of the main areas the Cubs want to see growth from Horton is in locating his slider and secondary offerings in the strike zone on a consistent basis.

They also don’t want to rush the 23-year-old right-hander, who has only made 11 starts in Triple-A and was limited to 34.1 innings last season.

Flexen has 110 career MLB starts under his belt, including 30 with the White Sox last season.