Leo Baptistao was forced to leave Rayo's March 21 win over Malaga due to discomfort in his right thigh, but the club remained optimistic that the player would be able to make a full recovery ahead of this Friday evening's La Liga clash against Eibar.
However, after spending the international break working diligently with the club's physios, the medical staff were forced to rule out Baptistao's return for this weekend and ordered the striker to allow the injury to heal for the next six weeks, later confirmed in an announcement on the club's website.
The loss of Baptistao for the next month and a half comes as a blow to Paco Jemez's squad, who were hoping the Atletico Madrid loanee would give in-form striker Alberto Bueno the ability to rest as they position themselves for a run at the final Europa League place.
The injury essentially ends a disappointing season for Baptistao, who has struggled with injuries and only scored seven goals in 23 La Liga contests, most of which came in one or two games.
Baptistao could still make a return for the final two games of the season against Cordoba and Real Sociedad.
Swansea have also been said to be interested by the Mirror, but the striker may be starting to develop a reputation for being injury prone having also spent much of the 2011-12 campaign on the sidelines.