Sampaoli is expected to replace sacked Argentina coach Edgardo Bauza, with the Argentina Football Association (AFA) keen to complete a deal ahead of next month's friendlies against Brazil and Singapore.
Ole newspaper reported earlier this week that Sampaoli would give a farewell news conference on Friday even though his release clause will not be paid until June 1.
But Castro told Sevilla's official website: "I've heard rumors that our coach will not be there, but of course he will because he is a professional and he has to be at the helm of Sevilla FC until the end of the season."
Sampaoli is under contract until June 2018 but can leave if his 8364;1.5 million release clause is paid. Castro has warned the AFA it will have to pay in full before he can leave.