The 27-year-old right-hander is 0-1 with a 5.48 ERA in 10 career games (two starts) with Kansas City and Chicago. He has 27 strikeouts over 21 1/3 innings, and he has a staunch advocate in Cubs manager Joe Maddon.
"I'm a Mills fan," Maddon told reporters. "When you see him on the gun, his stuff doesn't blow you away. He's got great pitchability. I've grown to appreciate and understand what he's all about.
"I have often said he's kind of a throwback '70s, '80s kind of guy. He's not going to overwhelm you with stuff, but he makes pitches, and hitters get bad takes like they do against Kyle (Hendricks) sometimes. I think, given the opportunity, this guy will surprise people."
Mills has faced the Reds once before in his career, allowing one run in 5 2/3 innings and drawing a no-decision.
The Cubs will try to bounce back after losing 6-3 in the series opener against the Reds. Chicago jumped to a 3-1 lead before Cincinnati scored the final five runs of the game.
The Reds will attempt to secure back-to-back wins for the first time since July 2-4.
Cincinnati right-hander Anthony DeSclafani (5-4, 4.26 ERA) is slated to make his 18th start of the season. He has walked 26 and fanned 90 over 86 2/3 innings this season, which marks a half-decade since he entered the big leagues with the Miami Marlins in 2014.
In 11 career starts against the Cubs, DeSclafani is 4-3 with a 3.84 ERA. He has walked 20 and struck out 58 in 63 1/3 innings.
DeSclafani is confident that he and his teammates can close the gap in the crowded National League Central standings.
"We all feel like we can win," he said in comments published by mlb.com. "We're a last-place team, but we're in this thing. This division is so tight and we're keeping it so close. Most of these games that we lost were by one run.
"I don't think that's a reason to be discouraged that we're in last. These little bit of games haven't gone our way early in the year, and that's why we are where we're at. We feel like we're a playoff team. We just have to fight back and creep up these standings slowly."
The Cubs will play their first game since acquiring catcher Martin Maldonado from the Kansas City Royals in exchange for veteran reliever Mike Montgomery, who recorded the final out of the 2016 World Series.
Chicago also placed catcher Willson Contreras on the 10-day injured list because of a foot injury.
Maldonado could help ease the blow with Contreras out.
"(He's an) established catcher in this league who does a lot of great things behind the plate," Cubs president Theo Epstein said in comments published by the Chicago Sun-Times. "Can really receive. Can really throw. ... A favorite of pitchers to throw to. Lot of experience. Lot of savvy."
--Field Level Media