Multiple sources are reporting that right-handed reliever Michael Tonkin is on his way to Minnesota to join the Twins bullpen.
Fien was one of three Twins that left Wednesday's game because of injury.
Fien allowed three runs on five hits Wednesday, including a home run to Miguel Cabrera.
"Casey's shoulder is still a little bit tender," Twins manager Paul Molitor told reporters after the game. "We're going to make sure we are on top of that. We're going to get it checked out."
Tonkin has had some success in the majors. He holds a 3.26 ERA in 34 career games with the Twins. He has also had a good season for the Twins Class AAA affiliate.