Shannon led the Sooners with 92 tackles in 2013 and was a second-team All-Big 12 selection.
University president David Boren released a statement Monday afternoon, saying, "The University is unable to enforice its process at this time. The University has and is taking every legal step possible to move this process forward.
"The University is currently seeking to enforce its decision so that it may be in compliance with federal law requiring responses by institutions to such matters in a timely manner. With the fall semester beginning August 18, time is of the essence."