For anyone that saw the hit, it was apparent.
Tyler Eifert had a dislocated elbow -- it was so apparent that, as soon as it happened, Bengals analyst Dave Lapham said with absolute certainty. Just look at the picture in this posting (sorry to anyone with weak stomachs). Without any public confirmation or diagnosis, at this stage, the Bengals believe that it's a dislocated elbow, according to Albert Breer with the NFL Network.
Bengals believe Tyler Eifert dislocated his elbow. That'd likely put him out for an extended period of time. Tough break for good young TE.— Albert Breer (@AlbertBreer) September 7, 2014
After hauling in the 14-yard reception with 3:41 remaining in the first quarter, moving Cincinnati to the Baltimore Ravens nine-yard line, Eifert laid on the field in obvious pain. He would finish the game with three receptions for 37 yards (which was third-most on the team).
As Breer points out, Eifert could be a candidate for the Injured Reserve list, but with a designation to return.
However, it should be noted that anyone joining the IR list with a designation to return, is ineligible to practice for six weeks and won't be able to play for eight weeks -- Eifert would be out until week 9-10 (depending on when he's actually placed on that list). It's entirely possible that if there was no ligament damage or swelling, Eifert could return sooner rather than later. And it's entirely possible that Eifert could be out for the rest of the year.
More will be known as the week unfolds.