The Spaniard spent a season on loan at Derby.
Julen Lopetegui is a candidate to take charge at the City Ground.
The former Derby County loanee has struggled to find form at Porto.
The former Real Madrid trainee is the joint highest Spanish scorer in La Liga.
Spanish forward Alberto Bueno is out of contract with the Spanish club, at the end of the current season.
Three points were earned by Rayo Vallecano away at Eibar in La Liga, thanks to goals from in-form Alberto Bueno and towering Angolan striker Manucho.
Alberto Bueno is in terrific form this season and is out of contract in the summer.
Southampton are reportedly interested in signing Rayo Vallecano striker Alberto Bueno.
The forward scored four goals in 15 minutes yesterday afternoon.
The Spanish forward was sensational for Rayo Vallecano against Levante this afternoon.