CHICAGO -- The Cubs have been sorting through a series of complications to piece together a rotation for the next few days. A recent setback with right-hander Adbert Alzolay only compounded the situation.

Prior to Monday's doubleheader with the Cardinals, manager David Ross revealed that Alzolay was recently struck on his right forearm by a comebacker while pitching at the team's alternate training site in South Bend, Ind.

"Just a contusion," Ross said. "I've seen a picture. Looks like just a line drive off the forearm -- in the meaty part of the forearm. We're taking precaution, making sure he's all right. And we'll continue to listen to the trainers on that end."

That prompted Monday's decision to promote righty Tyson Miller from South Bend to serve as both the 29th man for the twin bill and the starter for Game 2 against St. Louis. Miller threw two innings in the 5-4 win, allowing two runs on one hit (Brad Miller's solo homer) and walking three.

Miller was selected in the fourth round of the 2016 MLB Draft by the Cubs and is the team's 25th-ranked prospect, per MLB Pipeline.

Between Double-A and Triple-A in '19, the 25-year-old Miller posted a 4.35 ERA with 123 strikeouts and 43 walks in 136 2/3 innings. He was added to Chicago's 40-man roster over the offseason.

Righty Tyler Chatwood was originally scheduled to start the second game on Monday, but a mid-back strain landed him on the 10-day injured list on Sunday. Prior to that, Chatwood was scratched from an outing on Friday, forcing the Cubs to move Alec Mills up in the rotation and pull Colin Rea out of the bullpen for a start on Saturday.

Yu Darvish is slated to start on Tuesday, with Mills taking the ball in one of the doubleheader games against the Cardinals on Wednesday. Rea could be an option for the other game, but Ross' preference is to keep Rea in the bullpen. Alzolay has also not been ruled out for a start on Wednesday.

"Yes, [Alzolay] is an option," Ross said. "But obviously, the throwing forearm is an important area, so it is a day-to-day thing, just with communication with the trainers. But he is still an option for Wednesday."

Worth noting
• Shortly before Monday's doubleheader, the Cubs scratched outfielder Steven Souza Jr. from the Game 1 starting lineup due to a tight right hamstring.

• The Cubs entered Monday leading the Majors in pitches per plate appearance (4.25), but deep counts can naturally lead to higher strikeout rates. Along those lines, Chicago's offense also had the highest strikeout percentage (27.9 percent) in MLB and the 25th-ranked contact rate (72.6 percent).

"I don't think they have to be a great contact group, no," Ross said. "We've got power up and down the lineup. Contact isn't always a great thing. Weak contact doesn't mean anything. I want the guys to drive the baseball.

"We want contact valued with guys at third, less than two outs, moving a guy from second. If there is a potential hit-and-run that I might put on, obviously contact's valued. But I don't necessarily value the contact just to make contact."

• Left-hander José Quintana (10-day injured list, left thumb) logged four innings and threw around 60 pitches in a simulated game at South Bend on Sunday. Quintana's schedule is still being finalized, but Ross noted that he will have at least one more sim game.

"I talked to him this morning, he said he felt great," Ross said on Monday. "All things seem well and good."

• Jason Heyward was scratched from Sunday's game with the Brewers due to tightness in his mid-back, but he was on the mend on Monday morning, per Ross. Heyward was back in the lineup in the nightcap, starting in right field and going 0-for-2 with a run scored.

Quotable
"I got the kids in town, and so online schooling started at 7 a.m. this morning, speaking of losing sleep. That was definitely different." -- Ross, asked if he lost any sleep after losing three games in a row