Hughie Morrison had been undecided whether to run the eight-year-old, who is lightly-raced over hurdles after a successful Flat career.
He won his last start at Ascot by nine lengths off a low handicap mark - yet despite a 17lb rise, he has been towards the head of the betting ever since.
Morrison is hoping his charge makes up into a Champion Hurdle contender.
In an open year for the Cheltenham showpiece, victory in Saturday's big handicap - for which he would also win a £100,000 bonus - would put him right in the mix.
Johnny Burke has been on board Not So Sleepy this season and said: "The Betfair Hurdle is a much bigger test than what we faced the last day at Ascot. The horse seems very well, and he schooled well the other morning.
"What he did at Ascot was a bit breathtaking - so with the 17lb hike, he is going to have to go and back it up now. It's going to be a tough ask - but I believe in the horse, and we will be going there with all guns blazing.
"He is a funny kind of a horse, who has his own way of doing things. When we kicked off the bend at Ascot I couldn't believe how well he picked up - I've never gone to the line in a handicap as easily as that.
"Whether he still has a bit of leeway on his mark, we don't know. We will find out on Saturday."
Gumball will carry top weight for Philip Hobbs, who also runs Oakley and Zanza.
Owner Terry Warner will rely on Gumball - with his Elixir De Nutz one of only two not declared from the five-day stage, along with Nick Gifford's Didtheyleaveuoutto.
Nicky Henderson's Never Adapt will aim to add to her trainer's good record in the race, along with Mill Green.
Nigel Twiston-Davies runs two novices. Rossington Main winner Stolen Silver and Sir Valentine.
Paul Nicholls is another with multiple chances - thanks to Pic D'orhy, Ecco and Tamaroc Du Mathan - while Evan Williams has declared the well-backed Mack The Man and Quoi de Neuf.
In-form Phil Kirby sends Whoshotthesherrif down from the north - while there is one Irish-trained runner, Willie Mullins' Ciel De Neige, ridden by Aidan Coleman.
Harambe, Thebannerkingrebel and Lightly Squeeze are others in the mix.