Usually after an ACL the repaired knee gets stronger, but having two injuries on plays that are pretty normal is not good.
My wife who is a PT, said it could be botched first surgery, or bad recovery, BUT it's most likely bad knee. She doesn't have his info, so it's hard to really say, but the way it happened she says the knee should hold up on those kinds of plays.
I love Parker, and would love to have him. He's got the kind of game that he doesn't need to be athletic, so the injuries doesn't scare me for his productivity, but it does for him actually being on the floor 70+ games a year. I'd want the medical records for the first surgery before I'd offer anything.