I don't think that it's just the bad knee. He's been taking too many Happy Meals under the belt.
As his weight has gone up from his breakout year, his ERA and WHIP have steadily risen for the past three seasons.
His fastball has slown down. He would throw 89 in the beginning of games and 92 at the end on fastballs. He would also have curl-back on his pitches from an elastic arm. Now he throws 85-87. And everything is pretty straight.
Putting him on a weight program (which would also help his knee) would help his pitching immensely.
As for his value, if he's not traded to a ballpark with a big OF, he could be sacrificing alot more runs and find himself yanked quickly. But I don't see the new owner selling a player the fans like, no matter how much he's booed. The DL as before suggested seems more possible, but Washington is running out of viable options in their Minor System.
My prediction...he'll stay with DC, he'll still be starting, and he'll still not be good a month from now. If you're in a league counting WHIP, I wouldn't even think about him. I'm sure Jason Jennings would even outperform Hernandez in the second half.