Paul Moloney world's most famous horse race with a third consecutive top four finish for bid as they will ride 11-year-old.
Williams said: "The reality is he is not good enough to win a National."
State Of Play in his last five races, four of the top four have ended in 2009 Hennessy Gold Cup at Newbury and Williams pulling for Grand National as it is saved from last April showpiece has not run.
But Vale of Glamorgan handler such as Midnight Club and a secret key claim about the possibility of death do not trust.
Williams said, "The first National I got very nervous because I think State Of Play had a serious chance".
"Last year I wasn't so bad because I thought his chance had gone and this year I'm being very relaxed because the reality is he is not good enough to win a National.
"He is carrying less weight because he is not good enough to win.
"As long as the horse comes back in one piece, that is all I can really hope for. Anything more than that is a bonus.
"You can never say never in a National because it can be carnage so you always have a chance. If he runs well and finishes respectably, I'd be happy enough.
"You would be very stupid to be too confident going to a Grand National. But I'm happy as we have done all he can do as we couldn't have got him fitter."