The nine-year-old is without a win since his Grade 2 Cotswold Chase success in January 2020 and will line-up for Friday's Grade 3 Betfair Handicap Chase, in which Harry Skelton will be on board for the first time.
Beaten a neck by Al Boum Photo last year's renewal of the blue riband, he has also won a novice hurdle at the track in addition to that Cotswold Chase success.
But having lost his way for Nicky Henderson last season - most recently pulling up in the Gold Cup in March - Santini was sent to join Gundry's small team in the hope it will rekindle his enthusiasm.
"I couldn't be happier with him. I'm nervous about his comeback and I think he'll come on in confidence for the run, but otherwise I'm very happy with where he is," said Gundry.
"All my horses come on for a run and he'll be no different, but we've done lots of different things with him - a bit of hunting, cross-country schooling - and I think he's in good nick.
"I'm satisfied that we might have got some more winter ground, rather than the ground we've until now, so I'm grateful that we've waited until the stage.
"He's a big horse, so hopefully he'll be able to carry the weight and have a nice run."
Santini is no stranger to his current home in Devon, having won a point-to-point for Gundry's husband Ed Walker in the spring of 2017.
Gundry added: "He went to Nicky Henderson's as a young horse and he said he was just too big and backward, so he came back to Ed and ran in a point to point at Didmarton and won really nicely.
"I thought a huge amount of him as a three coming four-year-old, when we had him in pre-training. Ed rode him all the time as he was such a big horse - even as a four coming five-year-old he was a big boy.
"We know him and he's fitted into our way of doing things really well.
"It's all very well enjoying the days out when Nicky's training him. I've thoroughly enjoyed having him and riding him, but when he's my responsibility it is different."
Santini must concede upwards of 12lb to each of his nine rivals, with the Paul Nicholls-trained Enrilo the likely favourite.
The seven-year-old turns out just under a fortnight after falling when well fancied for the Ladbrokes Trophy at Newbury.
"I was expecting a big run from him in the Ladbrokes Trophy at Newbury and he was travelling really well until he came down just after halfway," Nicholls told Betfair.
"He was fine afterwards, was quick over his fences when we schooled him on Tuesday morning, and good to soft ground will be fine for him.
"I'd say he has strong claims in a race that doesn't look particularly strong."
Other leading contenders include Fergal O'Brien's Badger Beers Chase third Hurricane Harvey and Pat Fahy's Irish raider Mister Fogpatches, who was last seen finishing third in the Troytown at Navan.