As Hildy noted in the FanPosts earlier, the Post-Dispatch's Jeremy Rutherford is reporting
tweeting that T.J. Oshie underwent an emergency appendectomy last night and will obviously be out indefinitely. No idea on how long these things brew before surgery is required or if it was the result of an injury, but details will surely follow soon.
Oshie's game is predicated on a certain fearless energy and reckless abandon whenever he's on the ice, something that has been missing a bit lately. Hopefully his recovery is quick and that his normal up-tempo game returns at the same time.