Castro detailed the talks on Friday, per Dan Sansom of Sky Sports: "Sevilla now need a sporting director and we have looked for the best, and the best is Monchi. Our conversations go well with him. The conversations have been very positive."
Bringing Monchi back to Sevilla would be a coup for Castro. It would also disrupt Arsenal's plans, as the Gunners are taking steps to hire the 50-year-old:
Bringing Monchi back to the Ramon Sanchez Pizjuan Stadium would generate excitement at a club seemingly adrift. He served as sporting director for 17 years before moving to AS Roma in 2017.
Monchi's spell in La Liga saw Sevilla win two UEFA Cups under manager Juande Ramos and three Europa League trophies with Unai Emery in the dugout. Both managers benefited from Monchi's astute eye for talent, which yielded bargain finds such as Frederic Kanoute, Dani Alves, Ivan Rakitic and Carlos Bacca.
Replicating the same magic in the Italian capital proved too much for Monchi, who stepped down earlier this month. Big-money signings like Javier Pastore didn't work out for the Spaniard, who initially ruled out a quick return to work despite heavy links to the Gunners:
Missing out on Monchi altogether would rate as an annoying setback for Arsenal. The north London club has been trying to hire some heavyweight scouting expertise since Sven Mislintat left after 14 months in the job as head of recruitment.
Monchi looks like an ideal fit thanks to his experience working with Gunners head coach Emery. However, Arsenal have other options, including Ajax executive Marc Overmars.
The Dutchman won the Premier League and FA Cup double as a key member of Arsene Wenger's squad in 1998. He's been linked with a return after developing several young talents in Amsterdam in recent years.
Bringing Overmars back would ensure the Gunners continue to promote attractive football and a fidelity to building through youth. Both were key tenants for 22 years before Emery replaced Wenger last summer.
Ironically, Emery's predecessor would also be an exceptional choice for a sporting director role. Wenger once ridiculed the title, but he has reportedly been considered for a similar role by Paris Saint-Germain.
Despite his misconceptions about the job, 69-year-old Wenger could surely handle unearthing talent for bargain fees, defining characteristics of his tenure. He prized spending within a club's means while still playing a progressive game, philosophies he could maintain while assisting Emery.
The Spaniard has been growing into the demands of replacing Wenger. He has Arsenal fourth in the Premier League and into the last eight of the Europa League.
Yet the Gunners' choice for technical director will do more than make Emery's job easier. It will also go a long way to determining the direction of the club in the immediate future.