"I don't know what the rehab will be like because I've never had anything like this," Pressly said. "It's a tough situation. I feel bad because I don't want to say I'm letting the team down, but it's an important stretch heading into the All-Star break and we want to get some momentum."
Pressly said he thought it was a shoulder injury initially, but that the MRI showed that there was no damage to his rotator cuff or labrum.
"Everything in the shoulder came back strong and healthy so that was good," Pressly said. "I just have to see how it feels after 15 days. I'm sure I'll need a rehab assignment or something."
The move is retroactive to Saturday, as Pressly didn't pitch on Sunday. Pressly has been solid this season, posting a 2.93 ERA with 22 strikeouts, 12 walks and no homers allowed in 27 2/3 innings.
Robinson, meanwhile, missed three games after being placed on the family emergency list for the second time this season. He flew to Boston to be with his 7-month-old daughter, Harper, who had successful surgery over the weekend. She was born with a stomach/esophageal condition that requires multiple surgeries.
Robinson is hitting .250/.303/.313 with three doubles, two triples and four stolen bases in 50 games. With Robinson replacing Pressly, the Twins are down to a 12-man pitching staff for the first time since May 22.
Rhett Bollinger is a reporter for MLB.com. 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.