MINNEAPOLIS — The Minnesota Twins have made some progress with their starting pitching this year. The rotation is ranked 10th in the American league in ERA, after finishing last each of the previous three seasons.

This is still an area of concern, though, with the Twins trying to stay viable in the AL wild card race.

The biggest problem, currently, is health.

Right-hander Phil Hughes will be put on the 15-day disabled list, retroactive to Monday, due to inflammation in his lower back. The decision was made Thursday, when Hughes was sent for a cortisone injection. The 29-year-old’s last start was his worst of the season: nine hits and seven runs allowed in three innings Sunday at Cleveland.

Then came his bullpen session Tuesday. That was quickly cut short because of the discomfort.

“Quite transparently, I knew nothing,” said manager Paul Molitor, referring to Hughes’ start against the Indians. “And I don’t think that anybody thought anything was going on until he got out there on Tuesday.”

The good news for the Twins was left-hander Tommy Milone’s bullpen session went well Thursday, clearing him for reinstatement from the disabled list Sunday to start against Cleveland. He will have missed the minimum 15 days because of a strained left elbow.

Rookie right-hander Tyler Duffey will be recalled from Triple-A Rochester and start Saturday against the Indians. Duffey gave up six runs in two innings last week at Toronto in his major league debut, but the front office was willing to give him another shot rather than summon top pitching prospect Jose Berrios.

Duffey has a 2.54 ERA in 138 minor league innings this year, between Double-A and Triple-A.

“He’s not going to be in the buzz saw of facing the Blue Jays in a difficult environment,” Molitor said, adding: “We just hope that the results are better and he can be a little bit more composed and be himself.”

The Twins also moved right-hander Trevor May from the bullpen back into the rotation to start Friday. He spent more than a month, successfully at that, as a reliever. May will be on a limit of roughly 50 pitches. Molitor said May will get a second turn, too, at Baltimore next week.

“Right now I don’t really want to turn him into a yo-yo man so to speak,” Molitor said. “I don’t want him to start two games and go back. We just have to see how it plays out.”

Ricky Nolasco remains on the disabled list following right ankle surgery.

“I’m sure he’s going to try to find his way back to an active role sometime before the season ends, but I couldn’t tell you how that’s going to play out,” Molitor said.