The Blackburn forward, who is wanted by the Premier League duo, is out of contract in the summer.
Both clubs submitted bids to Blackburn, but they were turned down, per Football Insider.
Now the source is adding that four clubs in Spain are set to offer Diaz a pre-contract in January.
While he can only join a team in the summer, he can sign a deal that will sort out his future this winter.
Blackburn would prefer to sell him in the January transfer window, but may not have much choice.