My guess is any sort of injury that may impact the health of his knees (and the quad is definitely that) the pats are going to take the most extreme measures of caution with, at least while he's still young and fresh.
There were intial reports after his IR'ing that he would have likely been fine to come back had this happened earlier in the season, but the timing of the injury and already ridiculous luck (bad) with injuries we had the team decided it was in everyone's best interest to shut it down (avoid rushing back) and use the roster spot on a fresh body.
Of course if this becomes routine, then enivitably the gamble the Patriots took will roll out snake eyes. At this point tho? The first year most people came to terms early on that it would be looked at as a red shirt year anyway..this past season he was a monster disruptor (hia stats won't reflect that but film will, as well as Chandler Jones/Jabal Sheards Production ). It's way to early to be hurling around the 'bust' word.