The four-times World Hurdle hero has been sidelined by injury since winning his 18th consecutive race in the Long Distance Hurdle at Newbury in December 2012 but is now just days away from his comeback.
Stewart said: “I’m not a little bit of a nervous owner, I’m a terrified nervous owner. He has been in the newspapers more than Simon Cowell recently. He’s a people’s horse and a lot of people will be rooting for him.
“It’s a big responsibility. He doesn’t know that, but I know that and I will be very nervous.”
Asked how sure he was that Big Buck’s is as good as ever, Stewart told At The Races: “This is where we’re going to find out.
“Everything he has been doing at home, the racecourse gallop that he had and the work Sam Twiston-Davies has done on him, is saying to the experts that he could be back to the form he was in when he won the race at Newbury in a common canter.
“Nobody in Paul Nicholls’ team is saying anything other than they think he’ll run a pretty good race on Saturday. Let’s hope so.
“He has had a phenomenal career. When it goes from two (wins in a row), to three to 16, 17 and then 18 at Newbury – he’s a pretty phenomenal horse. I’ll never have another one like him.”
Big Buck’s will face a maximum of 10 rivals in this weekend’s three-mile contest including last year’s winner and dual Long Walk scorer Reve De Sivola.
Willie Mullins has Boston Bob and Mikael D’Haguenet in contention, while the Rebecca Curtis-trained At Fishers Cross could look to get his season back on track following a disappointing first half of the campaign.
The Stewart-Nicholls combination also have Lanzarote Hurdle winner Saphir Du Rheu engaged, but he is unlikely to take his chance.
“You’ve got Reve De Sivola and At Fishers Cross. I believe Boston Bob is running at Gowran Park on Thursday. Saphir De Rheu won’t run unless it’s absolutely bottomless and we take Big Buck’s out,” said Stewart.
“There’s good old Mikael D’Haguenet as well. I’m very pleased they reopened the race and I’m pleased they’ve got 11 entries.”
Twiston-Davies will be partnering Big Buck’s for the first time in public and is already counting down the hours.
The jockey, who rode a treble at Leicester on Tuesday, said: “I can’t wait until Saturday.
“The entries came out today and there are 11 of them and eight or nine may turn up. After sitting on him the other day, I couldn’t be happier.
“I am looking forward to it. It is a nice position to be in because you are riding the best horse in the race. Do things right and hopefully it will work out.”
Welsh handler Evan Williams has entered Lienosus, who could make a quick reappearance after recording a facile victory under top weight in a handicap hurdle at Taunton on January on Saturday.
Williams said: “We will keep an eye on the Cleeve Hurdle for Lienosus, but I am not saying he is going to run.
“I can’t imagine there will be many runners and if he seems OK come declaration time, we will definitely keep an eye on it.”
Ballyglasheen could aim to prove last month’s Cheltenham victory was no fluke by returning to the track for Saturday’s JCB Triumph Hurdle.
The four-year-old claimed his third victory from eight starts over hurdles with a shock 33-1 win in another Triumph trial, but trainer Evan Williams is unsure about the strength of the form.
Ballyglasheen beat Kentucky Hyden by a neck, with Commissioned and Vicenzo Mio third and fourth respectively.
Williams said: “We will definitely have a look at the JCB Triumph Hurdle Trial for Ballyglasheen.
“He has been in very good form and has probably improved a bit since his win there last time.
“I was very surprised at Cheltenham and thought it was a very fluky performance, but I thought it was a poor race.
“The second, third and fourth horses are probably over-hyped and we were a little bit more streetwise.”