That is a blow to Michigan's secondary. Countess was the leading candidate to start opposite Jourdan Lewis, give or take a Wayne Lyons, and even in the event he lost the job he figured to see considerable playing time spotting various guys in the secondary.
Countess struggled mightily last year as Michigan transitioned to a man press style, but was an All Big Ten performer as a sophomore in a zone system. It is possible that Michigan apparently rededicating themselves to the aggressive system they had to ditch midseason last year may have precipitated a transfer. Either that or the usual transition stuff compounded by the availability of immediate eligibility elsewhere.