"It's kind of strange when you look at it as a positive, but I think it eliminates part of the mystery we've been dealing with for most of the year," Molitor said. "The uncertainty of when this occurred and the fact it went undetectable for a long time -- did it happen and then heal? I don't think we have those answers. But at least he knows this has a good chance to heal with rest."
May's back problems began last year when he was moved to relief in the second half of the season. He was placed on the 15-day disabled list three times this season with lower-back stiffness, despite his efforts to stay healthy with regular visits to the chiropractor, yoga and pilates.
May entered the year as a primary setup man for the Twins, but the 26-year-old finishes with a 5.27 ERA in 44 outings. He struck out 60 in 42 2/3 innings, but he also walked 17 and gave up seven homers.
With May's health issues as a reliever and Minnesota's lack of rotation depth, the Twins plan to have him head to Spring Training as a starting pitcher in 2017.
"We've talked a lot about how we want to potentially bring him back to start," Molitor said. "It's been tough for him. There were times in the year he was really good. Other things set him back, and obviously not being able to pitch very much this year doesn't help him in terms of gaining experience. I think there's at least some peace of mind that this is what it is and he can move forward."
• Minnesota third baseman Miguel Sano, who had been out since Sept. 13 with lower-back stiffness, returned to the lineup for Game 1 of Thursday's doubleheader. Sano was cleared after participating in baseball activities on Tuesday and Wednesday.
• Third baseman Trevor Plouffe, outfielder Danny Santana and left fielder Eddie Rosario will not travel with the Twins on their season-ending road trip next week through Kansas City and Chicago. The three will head home after suffering season-ending injuries.
Rhett Bollinger has covered the Twins for MLB.com since 2011. Read his blog, Bollinger Beat, follow him on Twitter @RhettBollinger and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.