The former Barcelona B product injured his shoulder in the opening-weekend draw at Derby this season and has barely featured for Rovers since coming back from three months out on the sidelines.
There were high hopes that Rochina, 22, could play a big part in Blackburn's future but he spent time out on loan at the end of last season too and with the Sky Bet Championship club despite to clear its wage bill, his move is no real surprise.
"Obviously we are seeing it as an opportunity for him him to go out to Spain and get games," boss Gary Bowyer told the club's official website.
"His injury on the opening day of the season set him back with us. So we've agreed it will be good to get him playing some games and we'll pick it back up in the summer.
"Playing in his native Spain appeals to Ruben, so we'll monitor his progress."