According to a statement by the team, Marshall underwent surgery to alleviate swelling and pressure not long after the injury.
On Thursday, Marshall was transferred to Barrow -- recognized internationally as a leader in neurological research -- where he will continue his recovery.
Marshall began this season with Arizona and made 13 appearances before being optioned to Reno in May.
Steve Gilbert is a reporter for MLB.com. Read his blog, Inside the D-backs, and follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.