MESA, Ariz. -- Wade Miley was encouraged by the live batting-practice session he threw for the Cubs on Sunday. The veteran pitcher checked out the data after his outing, liked what he saw and told reporters that things went better than expected.

That feeling did not last.

On Friday morning, Cubs manager David Ross revealed that Miley is currently dealing with inflammation in his left elbow. The veteran will begin the season on the injured list, delivering a late-spring setback as Chicago tries to map out its pitching staff.

"Not too concerned right now," Ross said. "We'll let that thing calm down and get him back started."

The plan right now is to have the 35-year-old Miley shut things down for a minimum of 10 days before being re-evaluated. Ross noted that the lefty did not feel discomfort while throwing, but rather during his windup, especially when elevating his arms. When the issue persisted, the Cubs had Miley undergo an MRI exam, which showed the inflammation.

There is no firm timetable for Miley's return, but the typical buildup program for a starting pitcher could mean the lefty is out of the mix until late April at the earliest. In the meantime, the loss of Miley to start the season will have a ripple effect on the Cubs' Opening Day roster.

Rotation ramifications
Miley was already on a slower program this spring, and it was clear the Cubs were building in some contingency plans. Behind Kyle Hendricks and Marcus Stroman, Chicago has been working on building up volume for a long list of arms.

"We've got multiple guys that are built up," Ross said.

Lefties Drew Smyly and Justin Steele, for example, are preparing for starting roles. The Cubs also have righties Alec Mills and Keegan Thompson going through a starter program this spring. All four pitchers in that group could be mixed and matched, or paired together, for April games.

Earlier this spring, Ross noted that Steele had a Minor League option, but the manager has since indicated strongly that the lefty will be in the Cubs' rotation. Smyly, while open to helping in relief, has also been told he is going to start.

Mills has a track record of performing better on a starter's routine (4.13 ERA when pitching with four or five days of rest) than as a reliever (5.24 ERA). Thompson had a taste of starting and relieving as a rookie in 2021 with mixed results (2.43 ERA in 26 relief outings vs. a 5.51 ERA in six starts).

It helps that the Cubs have an off-day after their season-opening four-game set with the Brewers. If needed, Chicago can delay using a fifth starter until April 16 in Colorado. And while Miley is out, the North Siders have multiple ways they can piece together their rotation innings.

"It's obviously terrible to have that happen," Hendricks said of Miley's injury. "But at least it's not worst-case scenario. At least he's just shut down for a little bit and, hopefully, he'll be back quick. But other than that, we have so many other options. Guys that we've signed or young guys that we've had in the org for a couple years now. A lot of guys can come in and fill that role."

Impact on the bullpen
The shortened runway to Opening Day has created a situation where plenty of teams are building bullpens in an unconventional manner. Having multiple relievers capable of throwing more than one inning is going to be crucial at the season's outset.

The addition of two extra roster spots to begin the year, plus the Miley setback, allows the Cubs to consider carrying three extra pitchers on Opening Day. That is important, given the fluid nature of Chicago's rotation at the moment.

"The 'pen guys, if I was counting through it," Ross said, "we probably have five or six guys that can go two-plus, so I think we're covered."

Mills and Thompson certainly fit that description. Lefty Daniel Norris and righties Scott Effross and Michael Rucker fall into that mix. Non-roster invitees such as Jesse Chavez, Robert Gsellman and Mark Leiter Jr. would also be multi-inning options.

The Cubs plan on taking a look at Leiter on Saturday, when he will make a Cactus League start against the Angels. The setback with Miley could make an NRI option such as Leiter (who boasts MLB experience) a late-spring dark-horse candidate for the Opening Day staff.

"That's real depth for us," Ross said of Leiter. "Something we haven't had in the past is some starter depth. He's a guy that's still competing and I think he ideally wants to start. But I think he can come in the bullpen and be a piece."