The revolving door in the Cubs bullpen continued Sunday when the team placed Alec Mills on the 10-day injured list and selected the contract of Tommy Nance from Triple-A Iowa.

Nance will be the 17th different pitcher the Cubs have used out of the bullpen already this year, but they’ve always known their pitching depth would be tested after the shortened season.

Mills’ injury is the latest in a stretch where the Cubs have been hit hard in that regard over the last couple of weeks.

He threw 1.2 innings in relief Saturday and reported some stiffness and tightness in his lower back after the game.

“[The trainers] don’t want to push it right now, this part of the season,” David Ross said. “He’s had it a little bit in the past and something they want to get on top of early. Just makes some sense.”

Nance, meanwhile, will get his first opportunity on a big-league roster. The 30-year-old went undrafted out of Santa Clara University and after a stop playing Independent ball in the Chicagoland area, the Cubs signed him to a deal before the 2016 season.

He has spent the last few years in the minor league system and was in big league camp with the team this spring.

Nance has excelled in Iowa so far this season, striking out 10 batters in 6 innings and allowing only 1 run on 1 hit and 1 walk.

“Great reports on Tommy — he’s got real velocity, he’s probably been throwing as good as anybody down there,” Ross said. “The breaking stuff’s real. Saw him in spring training, like what we saw.

“It’s an exciting arm — the velocity’s upticked in the time off and he started off the season really well. Somebody that I think can get significant outs for us.”

Nance began 2021 at the team’s alternate site in South Bend and is another name on a growing list of pitchers who have found a way to take their careers to the next level in the Cubs system.

Justin Steele and Keegan Thompson have come into their own as young pitchers recently but the Cubs also have a host of recent reclamation projects to hang their hat on — Rex Brothers, Dillon Maples, Jason Adam, etc.

The Cubs’ VP of pitching Craig Breslow has helped change the organization’s pitching infrastructure in his two years in the front office.

“Craig Breslow has really taken over our pitching department and done wonders,” Ross said. “The guys underneath him all have input and do a phenomenal job and you saw some of that pitch shaping, pitch characteristic stuff playing out in spring training.

“I would give a lot of credit to Craig and his changing the infrastructure of the pitching here and focusing a little more on pitch shaping and velocity.”

The Cubs hope hope Nance can follow in his teammates’ footsteps and make an impact in the majors.