Sanchez has very large hands, they don't help with his fumbling however.A QB handles the ball on every offensive play. Any physical characteristic (small hands) that would call into question his ability to handle the ball reliably is obviously a concern until it becomes not a concern.
Is it an "oh my God" concern at this point? No it is not but he does apparently have small hands for the position he plays and he does have for whatever reason, a record of putting the ball on the ground at a high rate. Those are facts. Those are measurable metrics. They are not invented.
At the NFL level the number of things which will affect the QB's ability to do his job properly and the speed at which those thing happen is magnified immensely. If your team has a weakness, any weakness that can be exploited, especially at the QB position, then you can be sure that defensive coordinators are going to game plan for that.
Do I think that a QB with big hands is a lock to be a great QB? No, of course I do not. Do I think that a QB with very small hands can never be a successful QB in the NFL no matter what? No, I don't think that but what I do believe is that that all other things being equal, larger hands give a physical advantage to a QB.
So am I concerned? Yes, I am concerned a little. Am I worried sick over this? No I am not. But to declare this as a non issue without any evidence that his fumbling is behind him is nothing more than wishful thinking at this point.