Evan Williams thinks his Grand National hope State Of Play is "not good enough" to win Saturday's Aintree marathon.
Paul Moloney will ride the 11-year-old as he bids for a third successive top-four finish in the world's most famous horse race.
The 25-1 chance has not raced since finishing third in 2010 and is carrying five pounds less at Aintree this year.
But Williams said: "The reality is he is not good enough to win a National."
State Of Play will carry 10st 6lb in the 40-strong field that will line up for the four-and-a-half mile handicap chase over demanding fences such as Becher's Brook and The Chair.
The gelding has been Welsh trainer Williams' only Grand National runner and finished fourth on his debut in 2009 before a third-placed finish in 2010 when Tony McCoy famously won on Don't Push It.
State Of Play has finished in the top four in four of his last five races - pulling up in the 2009 Hennessy Gold Cup in Newbury - and has not run since last April's showpiece as Williams has saved him for the National.
But the Vale of Glamorgan handler is not confident about his chances of beating leading contenders such as The Midnight Club and Backstage.
"The first National I got very nervous because I think State Of Play had a serious chance," said Williams, bidding to become the first Welsh-born trainer to win the National since Nigel Twiston-Davies saddled Bindaree to victory in 2002.
"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."
Williams has decided to run Deep Purple against 2008 Cheltenham Gold Cup winner Denman in the Totesport Bowl at Aintree on Thursday.
Moloney will ride the 10-year-old in the six-strong field for the 3m 1f race.