If the reason he is not the long term answer injuries, then even then I don't know if I'm ready to call Tua injury prone.
Though football is a violent sport, those are two vicious hits. Hits like that don't happen that commonly, Brady rarely takes shots like that, because of how much he's protected.
Right now it's been some bad luck for Tua, along with an O-line that is a work in progress, and Tua still learning that getting rid of the ball or just taking the safer, shorter play, and living to see another play is not a fail.
Tua before that Bengals hits, with that to great anticipation and accuracy, along with one of the quicker releases in the NFL was looking not like a top 10 QB, but top 5...Tua has to clean up a few things, but he definitely is the long term franchise QB Miami has been looking for all these years since Dan retired.