I think it's a little sad every year that people miss training camp, don't learn their new job and don't perform well in their rookie season. We see it with Jamarcus Russell, and alot of other high profile guys. I've heard that they may make a rookie salary cap, or wage scale, but if they don't here's another solution.
When a guy gets drafted, why not sign him to a soft agreement. A piece of paper which states he will make between A and B amount, and in between X and Y years. This way if a team wants to sign a guy for 5 years and 30 million, and he wants 4 years and 26 million, they can draw up a soft agreement that this player will still come to camp on time, and participate in all the off season events, while still negotiating between these terms. If the guy gets hurt, it he is still guaranteed to get a contract valued between the parameters of what the two sides agreed on.
Salaries could be negotiated, players wouldn't lose any time, and they would be guaranteed a contract even if some injury should occur.