That's a concern, as the NFLPA is giving him guidance and some think that they are part of the reason why he's asking for a 100% guaranteed deal, the players want the NFL to become more like the other leagues.
The reports I read said that his knee just wasn't healing. It was a PCL sprain, which tend to be on the milder side of knee injuries, but sometimes it happens. I don't question his toughness. Reminds me of Sam Bradford...
However, there was some scuttlebutt that other players on the team were frustrated with him, and I believe he didn't show up to their playoff game in January... lol, there's an article about Michael Vick calling him out for it. There seems to be more going on behind the scenes.
That is true, though Mark Andrews is a stud. Their plan at WR last year was dumb, they need to go heavy on investing in WRs. Good thing it's a historically bad WR crop in free agency and a below-average WR crop in the draft...