Why Yankees traded Jordan Montgomery to Cardinals for Harrison Bader

A day after trading for Frankie Montas to bolster their rotation, the Yankees subtracted one of their most consistent starters just before the trade deadline.

The Yankees sent lefty Jordan Montgomery to the Cardinals on Tuesday in exchange for outfielder Harrison Bader and a player to be named later or cash considerations.

Bader is currently on the injured list with plantar fasciitis and in a walking boot. That could delay his Yankees debut until September, general manager Brian Cashman said. When Bader is available, the Yankees will get a strong defensive center fielder and speed threat who is also under contract through next season.

But it came at the cost of Montgomery, the homegrown pitcher who was visibly emotional and still in shock about an hour after the trade went down.

“I didn’t acquire Montas so I could move Monty,” Cashman said after the deadline had passed. “Me and my staff entered the trade acquisition market of exports and imports trying to figure out the overall ecosystem of that roster and what fits best with a plan for October and how could we best be flying high at the best of our abilities when it counts the most in October and what gives us the most amount of quality choices? That’s what went into every single decision we made.

“So we’re excited about what Bader can bring down the line for us. We have to wait on it, we get that. But it came at the expense of a quality choice we already had.”

The trade capped off a busy few days for Cashman — who filled holes in left field (Andrew Benintendi), the rotation (Montas) and the bullpen (Scott Effross and Lou Trivino) while also trading Joey Gallo to the Dodgers.

“The biggest part of it is just kind of that sadness of seeing a guy [leave] that you love and that you’ve been through a lot with and that’s done a lot for this team and organization,” manager Aaron Boone said after an 8-6 loss to the Mariners. “Coming out of nowhere today where that happens, it’s hard delivering that news and saying goodbye.”

Even after acquiring Montas from the Athletics on Monday, the Yankees continued to explore adding another starting pitcher before the deadline, Cashman said. The Post’s Joel Sherman and Jon Heyman reported that the Yankees were in on Marlins right-hander Pablo Lopez, though a deal never came to fruition.

Instead, the Yankees will move forward with a rotation of Gerrit Cole, Montas, Jameson Taillon, Nestor Cortes and Domingo German before hoping that a healthy Luis Severino joins them in mid-September when he is eligible to come off the 60-day IL. They also have another option in Clarke Schmidt at Triple-A, though they gutted much of their starting depth beyond that in trades over the last few days.

“I’m confident [in the rotation],” Cashman said. “My job is always to worry, but I believe in the guys we have.”