He thought the injury was minor, as he was still able to throw five scoreless innings to help lead the Dominican Republic to the title, but felt it while throwing a bullpen session on Thursday.
Gardenhire said there is no timetable for Deduno's return and that right-hander P.J. Walters will start in his place against Toronto on Sunday.
"We have to wait until he's healthy," Gardenhire said. "We don't have a plan until he gets back on the mound. He has some groin tightness. We put him on the mound, but he said he felt something at the World games so we're just biding our time now."
Deduno was a candidate to be part of the club's starting rotation, especially after he posted a 0.69 ERA with 17 strikeouts and five walks in 13 innings in the Classic.
But now it appears that the non-roster invitee will have trouble being ready for the season. Other candidates for the back end of the rotation include Liam Hendriks, Cole De Vries and Walters.
"He didn't think it was a big deal, but it is a big deal because you can't start with that," Gardenhire said. "So now we're on hold until he gets back off that. It kind of makes us ad lib a little bit."
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.