Sakho is on a season-long loan at Elland Road from Marseille along with team-mate Salomon Olembe. Both are on African Nations Cup duty with their countries.
Leeds owe Marseille for their loan transfers and if they do not receive any money they could do a deal with the Spanish clubs for Sakho.
Meanwhile, another loanee, Zoumana Camara, could be set for a move back to France.
Wolves and Bolton have been interested in the French defender along with Bastia, but it appears Camara has started talks with Strasbourg.