The left back has been linked with a switch to Brendan Rodgers’ side and narrowly missed out on a place in Spain’s 23-man World Cup squad.
Castro insists the club would be open to granting Moreno a move to Anfield but is adamant the 21-year-old will not leave in a cut-price deal.
"It's true that there's interest from Liverpool and we're waiting to see if that turns into a reality, which right now, it isn't," Castro told the club's television channel. "What I'm clear about is that we'll not force anyone to stay at Sevilla.
"Whoever wants to leave can do so, but we'll be the ones setting the prices. This club is experiencing a time of economic stability and we don't need to sell. We're going to be firm about this and we'll only consider selling outside the market, which gives us the opportunity to make our team competitive."
Having already secured a deal for Southampton striker Rickie Lambert, Liverpool has also submitted a final 25 million pound bid for Adam Lallana.