Mariano left Real Madrid for Lyon in 2017, was expected to move to Sevilla in a club-record deal after the Andalusian outfit reportedly agreed a €35m transfer.
However, on Monday it was revealed that Real exercised their first-option clause for the Dominican Republic international as the looked to bolster their attacking options that have been depleted since the exit of Cristiano Ronaldo.
In the same vein that Alvaro Morata returned to Los Blancos with increased experience and influence after Juventus, Sevilla president Castro has confirmed their domestic rivals have hijacked the sensational deal.
"We are an ambitious club and things like that happen when you want players of this level. It is true that Madrid had a preferential option and told us that they will exercise it but we still do not have the player's notification," Castro told reporters on Tuesday.
"The player told us he wanted to play at Sevilla, that he wanted to play in the Spanish league and, above all, that he wanted to play in a team who have won so many Europa League titles as Sevilla. He has not given an answer and we are waiting for his answer. You can guess [his decision] but we do not have a reply from the player who is the one who is able to say one thing or another.
"Sevilla have acted as we had to act. We have reached an agreement with Lyon. The footballer told us he would only play for Sevilla. They [Real Madrid] have considered to exercise their option."
Mariano scored 21 goals in 41 appearances for Lyon last season.