Pineda has been the most dependable starter for the reeling Twins with a 2-2 record and a 2.79 ERA in seven starts. Bailey Ober was recalled from Triple-A St. Paul and made his major league debut starting in place of Pineda.
Ober went four innings, allowing four runs on five hits with four strikeouts in a no-decision. The Twins rallied to win 5-4.
Pineda is being pushed back in the rotation and could start later in the week, manager Rocco Baldelli said.
"It's in a pretty uncomfortable spot for him," Baldelli said. "Something that's been around for a little while; it's gotten worse. And he had to have a little procedure to get that taken care of. So he's got a couple of stitches."
The plan is for Pineda to throw on Thursday to determine when he'll make his next start.
Ober, 25, was a 12th round draft pick by Minnesota in 2017. The 6-foot-9 right-hander had allowed one run in seven innings for St. Paul this season. To make room on the 26-man roster for Ober, the Twins designated Derek Law for assignment or release.
Minnesota also recalled right-handed reliever Cody Stashak from Triple-A and placed Shaun Anderson on the injured list with a left quad strain.
The Associated Press contributed to this report.