CHICAGO -- On the eve of a doubleheader with the Cardinals, the Cubs are still sorting out their pitching, given the latest setback with starter Tyler Chatwood.

Shortly before Sunday's 6-5 loss to the Brewers, the Cubs announced that Chatwood has been placed on the 10-day injured list with a mid-back strain. One day earlier, manager David Ross expressed optimism about Chatwood's ability to start one of Monday's games at Wrigley Field against St. Louis.

Kyle Hendricks will start for the Cubs in the opener of Monday's twin bill, which is scheduled to begin at 4:15 p.m. CT, but the Cubs have yet to announce their planned starter for the nightcap. Ross noted that he and the front office were meeting after Sunday's loss to go over that decision.

"As a staff, anytime somebody goes down, you try to pick them up," said Jon Lester, who worked six innings in Sunday's game. "We've got a long week ahead of us with some doubleheaders and such, so I knew coming in that I was trying to get a little deeper in the game than that. Unfortunately, I was not able to."

With Chatwood moved to the injured list (retroactive to Thursday), the Cubs selected the contract of right-handed reliever Jason Adam from the team's alternate training site in South Bend, Ind. To open a spot on the 40-man roster, Jharel Cotton was designated for assignment.

Chatwood was scratched from Friday's scheduled start against the Brewers due to back tightness, forcing Alec Mills to move up one slot in the rotation. Reliever Colin Rea then came out of the bullpen and started in Saturday's 6-5 loss, giving the North Siders 49 pitches over 3 1/3 innings.

Prior to Saturday's game, Chatwood played catch in left field with members of the team's medical and training staff monitoring the workout. Ross chatted with Chatwood about the throwing session and all the initial feedback made it seem like the righty was on target for a Monday return.

Things changed quickly on the Cubs prior to Sunday's game against the Brewers, as Chatwood reported lingering discomfort. That throws another complication in the upcoming plans for the Cubs, who have doubleheaders on Monday and Wednesday as part of a five-game, three-day series with St. Louis.

Yu Darvish would be on schedule to start Tuesday with Mills on target for taking the ball in one of Wednesday's games. Chicago's top rotation options in South Bend include righty Adbert Alzolay, Tyson Miller and Justin Steele.

José Quintana (left thumb) is on the 10-day injured list and was scheduled to log four simulated innings in South Bend on Sunday. Ross said earlier this weekend that Quintana still felt he had things to iron out and the lefty was not considered an option for the series with St. Louis.

Through three starts this season, Chatwood has posted a 5.40 ERA with 23 strikeouts against four walks in 15 innings. The righty was sharp in his first two outings, allowing just one run with 19 strikeouts in 12 2/3 innings. Then, Chatwood gave up eight runs on 11 hits in 2 1/3 innings on Aug. 6 in Kansas City.

The 29-year-old Adam joins the Cubs after being added on a Minor League contract over the offseason. The righty spent 23 games with the Blue Jays in '19, turning in a 2.91 ERA with 18 strikeouts and 10 walks in 21 2/3 innings.