Barcelona's problems with Samuel Umtiti, who is in Qatar taking treatment on his knee cartilage problem, means they are looking at buying a centre-back in January.
They would like Ajax defender De Ligt, but cannot sign him until the summer. So the club are looking at an emergency signing in the winter window.
One one hand they are negotiating with veterans who can sign a six month deal. On the other, young defenders with potential who could do more at the club over a longer period.
On the list is Branislav Ivanovic, the 34-year-old Serb at Zenit, Benedikt Höwedes (30), who is in Russia too with Lokomotiv Moscow, Portuguese José Fonte (34), at Lille, or Frenchman Adil Rami (32), at Olympique Marseille.
Among those younger ones with potential are Unai Núñez (Athletic), Diego Llorente (Real Sociedad), Jorge Meré (Koln), Milan Skriniar (Inter Milan), Leonardo Balerdi (Boca Juniors), Dayot Upamecano (Leipzig), Abdou Diallo (Borussia Dortmund) and Andreas Christensen (Chelsea). They would require more funds.
Other alternatives are Djené Dakoman (Getafe), or Belgian Toby Alderweireld, whose contract ends with Tottenham in June.