There are some out there who say that the Redskins do not have to make a choice between signing Peyton Manning in March and making a deal to move up and draft Robert Griffin III in April. That way, Griffin could learn under one of the greatest quarterbacks ever and take over when Manning rides off into the sunset (hopefully with one or two more Super Bowl rings on his fingers).After all, the Redskins wouldnt have to give up any draft picks to get Manning. With the new rookie salary structure it will take a minimum amount of salary cap manipulation to fit both Griffin and Manning under the cap.Sounds good but unfortunately, there an obstacle in the way. The NFL owners giveback in exchange for lower salaries to the top draft picks is that the contracts will be shorter. First-round draft picks now sign four-year contracts instead of the six-year deal that used to be common.So lets say the Redskins sign Manning, who just turned 36. The Redskins likely would be thinking of having him play for 3 years, giving him enough time to get fully adjusted to his new surroundings and teammates and then a couple of years to make a serious run at a title. That would mean that Griffin would be the backup for three years of his four-year contract. That hardly would seem to be a smart use of what likely will be two first-round picks, a second, and possibly other assorted selections.It is true that there would be a club option for a fifth year. However, the Redskins would have to exercise that option prior to Griffins fourth season. That means that they would have to fully guarantee a fairly substantial salary for Griffin before he ever took a snap as the starter.Perhaps Manning doesnt plan on playing for that long or maybe the Redskins could give Griffin a contract extension after two or three years. Still, it would be awkward to have a talent such as Griffin sitting on the bench for more than half a season or so, not to mention the fact that the Redskins would be without additional draft picks they could use to build a team around Manning.The bottom line is that Griffin and Manning is an eitheror proposition. There are pluses and minuses to both approaches and risks in both. But the Redskins are going to have to pick one and leave the other behind.Rich Tandler blogs about the Redskins at www.RealRedskins.com. You can reach him by email at RTandlerCSN@comcast.net and follow him on Twitter @Rich_Tandler.