Infantrycak - I feel obligated to correct my earlier post since I made several errors. Checking a ND website, you are correct that in 2013 Nick Martin injured his knee in the first quarter against BYU and missed the Stanford game (Not a ND fan, so I don't know if he missed a bowl game as well). Anyhow, his 2013 season ended early with ACL surgery and rehab. He missed all of 2016 rookie season due to an ankle injury, not a knee. However, I correctly stated that he played impaired in 2014 with a hand injury (also from a ND website).
Point being, injuries happen and the NFL uses IR to stash players, especially developmental players that they do not want to put on the practice squad where they are exposed to another team picking them up. At this point in either player's career, I would not say it is fair to call either injury prone, but this season is where they will have to prove that they aren't.
BTW, I just want the best team on the field, be it composed of late draft picks, high draft picks or free agents. I hope this team never resorts to "secret practices selecting players" and "playing the biggest check" ever again.