After departing McLaren at the end of last year's championship, Ricciardo is taking a sabbatical from F1 this season as Red Bull's third driver behind champion Max Verstappen and Sergio Perez.
The eight-times grand prix winner, one of the sport's most popular characters, had "thrown himself" into his new role, Horner said at the Australian Grand Prix on Friday.
"I’d say he’s about 10 minutes away from being ready (to race)," added Horner.
"He’s in good shape. He's kept himself fit and well. He's training hard and he's ready to go if given a chance.
"It must be very tough for him not being a race driver this weekend, but he’s thrown himself into and embracing this new role.
"Hopefully he'll rediscover his love for the sport."
Ricciardo claimed seven of his eight race wins during his 2014-18 stint with Red Bull before a barren two years at Renault and two difficult seasons with McLaren.
The 33-year-old has not decided on his future but told media at Albert Park "the signs are pointing towards getting back on the grid".
"I feel like that’s currently where I’m tracking, at least in my head and just a little few other habits that I’m having or doing is pointed towards that," he said.
F1 team bosses said Ricciardo would generate plenty of interest if he was motivated to return to racing.
"Everybody is wanting to speak with Danny after a year off, maybe he knows again what he wants to do and he will be interesting for everybody in Formula 1," Haas team principal Guenther Steiner told reporters.
Alpine team principal Otmar Szafnauer confirmed his outfit had discussions with Ricciardo last year about bringing him in for the 2023 season before opting for Pierre Gasly.
"I think, like Guenther does, he's a fantastic racing driver, he's still young and I wouldn't be surprised if he's back racing in the future," he said.
