May said the back issue cropped up on Thursday and is similar to the back issues he dealt with last season. The reliever missed six games late last September with the same injury.
"It just happened after I got back from Oakland," May said before the game. "It's the same thing [as last year]. I just don't think I addressed it properly in the offseason. So I'm just trying to get ahead of it. I had been throwing a lot. The long flight probably didn't help. But I'm just being cautious. It feels a lot better."
May pitched in four straight games before suffering the injury, posting a 2.45 ERA over that stretch, with seven strikeouts and one walk in 3 2/3 innings. May has been racking up strikeouts this year with 40 in 26 2/3 innings, but he has also served up five homers and thrown six wild pitches, which has led to his 5.06 ERA.
• Center fielder Danny Santana, on the 15-day DL since May 30 with a left hamstring strain, has progressed to running drills. Twins general manager Terry Ryan said Santana has been running at about 70 percent, but that it's a good sign he's been able to do that only about a week after suffering the injury. Santana is eligible to be activated on Tuesday, and the Twins are hopeful he'll be ready to return around that date, but he's likely to go on a rehab assignment.
• Right fielder Miguel Sano remains behind Santana in his recovery from his left hamstring strain, as he's still receiving treatment and isn't ready to start running drills. Sano, on the DL since May 31, is considered at least a week or two behind Santana.
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.