I would guess it's concurrent. If he torn his ACL the week the suspension came down, the clock on the suspension wouldn't be delayed starting until after he was able to play.Everybody agrees with that. The question at hand is does he get to play the entire junior year or miss the first 6 games of that junior year. Are the 1 year drug suspension and 1 year transfer rule served concurrently or consecutively. No where in the NCAA bylaws does it state that one has anything to do with the other except that he has to be enrolled in school for one calendar year before playing.
Plus the NCAA doesn't consider the year of ineligibility for a transfer a punishment, but a chance for the player to adjust to their new environment.
That all said, if its not in the rules its a grey area and the NCAA can probably do whatever they want.