At this point, I wouldn't spend the roster spot.
After the hit that caused Avril's injury, he was apparently experiencing numbness in both arms all the way down to his hands. Neurologists have said that, in such cases, full recovery of the damaged vertabrae and nerve bundles typically requires 1-2 years, and that the injury consequences from a second injury before healing is complete are "severe".
Avril was injured about six months ago and had surgery about two weeks after that.
Shea McClellin had suffered at least four concussions (that were reported) in his career prior to joining the Pats. Apparently, he had another concussion in Camp last year that put him on IR-return status. While he was practicing to return in mid-season, apparently concussion symptoms returned, and he was shut down for the remainder of the season.
He was released by the Pats on March 19th, "failed physical."
At some point, teams need to draw the line with some of these guys who want to come back from certain injuries.