Reports in the British media have suggested that last season's Premier League runners-up are set to complete a £16 million move for the 22-year-old.
Castro has revealed that negotiations have taken place with the Merseysiders in the past fortnight and concedes that the Spain international will leave if his valuation is met.
However, that has yet to happen and Castro claims to be comfortable with the situation.
"There have been negotiations [for Moreno], eight or 10 days ago, but there has been no agreement and nor is there today," Castro told the club's official website on Monday.
"If Liverpool's offer is suitable he will leave. If not, he'll stay and nothing will happen, absolutely nothing. We'll be at ease."
Castro also stated that no offers had been received for striker Carlos Bacca, amid reports of interest from Russian Premier League side Zenit.
He added: "I'm not aware of anything with Bacca. I don't listen to the rumours and they're not true, at least not that the club is aware."
In terms of incomings, Unai Emery's men are still searching for a long-term replacement for midfielder Ivan Rakitic, who joined Barcelona earlier in the close-season.
Valencia's Ever Banega has been touted as a possible Sevilla target, but Castro is willing to be patient in his pursuit.
"The coach knows what's necessary. I'm sure someone will join before the end of the market. No rush," Castro continued.
"There will be a creative player coming in midfield. Banega is an option but so are many others."
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