The Cubs said earlier in the day that Clevenger was expected to miss at least six weeks and would be placed on the 15-day DL when Darwin Barney returns from a deep cut on his left knee.
That plan changed.
Instead, they put him on the 60-day DL to make room for Loe, who has pitched in parts of nine seasons with Texas (2004-08), Milwaukee (2010-12) and Seattle (2013). Loe was 1-1 with a 10.80 ERA in four relief appearances with the Mariners before being designated for assignment on April 11.
Clevenger has appeared in eight games and has one hit in eight at-bats. He injured the left oblique muscle and fell to the ground in pain when he struck out to end Saturday's loss to San Francisco.
"As soon as I did it, I knew what it was," said Clevenger, who missed a month last season because of a right oblique strain. "It was a lot worse than last year, pain-wise. Last year, I did it in the last swing of (batting practice). I went up into the clubhouse and I was a little tight. But (Saturday), I just felt like someone stuck a knife in my side and knocked the breath out of me."
Gregg was 3-2 with a 4.95 ERA for Baltimore last season. He was with the Los Angeles Dodgers in spring training and was assigned to their minor league camp late last month.