Pelfrey maintained after his start that he was healthy but told Twins manager Ron Gardenhire on Friday that he was dealing with a groin injury. The Twins are hopeful the rest will help Pelfrey regain his velocity, as his fastball is averaging 91 mph compared with 92.4 mph last year, according to Fangraphs.com. Pelfrey has also struggled with his control, walking 18 batters in 23 2/3 innings.
"He came in today saying his groin was bothering him," Gardenhire said. "He tweaked it yesterday and didn't want to make any excuses. He came in today sore. We told him this might give him an opportunity to get his leg well. And then he can go on a rehab assignment and try to get it straightened out. So it's two-fold, get healthy and also figure out why his velocity has dropped down."
Deduno will move from long relief into the rotation to take Pelfrey's place. Deduno has a 2.89 ERA with 18 strikeouts and nine walks in 18 2/3 innings. He also threw 64 pitches in relief for Pelfrey on Thursday. Deduno made 18 starts last year, posting a 3.83 ERA with 67 strikeouts and 41 walks over 108 innings.
"We like what he did last year at times, so we'll see what happens," Gardenhire said. "We'll go from there."
Gardenhire added that outfielder Oswaldo Arcia was not recalled from Triple-A Rochester because he was still on a rehab assignment. Arcia has been on the DL with a right wrist strain since April 5. Infielder Eduardo Nunez is also still at Rochester with an oblique strain.
So the Twins went with Santana, who is rated the club's No. 10 prospect by MLB.com. He was hitting .268/.311/.381 with seven doubles and four stolen bases in 24 games at Rochester.
"After a slow start he swung the bat better," Twins assistant general manager Rob Antony said. "We were just trying to find the right fit. Arcia would've been ideal as a bat on the bench, but he needs at-bats and more time down there."
Rhett Bollinger is a reporter for MLB.com. Read his blog, Bollinger Beat, and follow him on Twitter @RhettBollinger. This story was not subject to the approval of Major League Baseball or its clubs.