Boro also have been linked with Standard youngster Axel Witsel, though his price-tag is likely to frighten them off.
The Evening Gazette says Boro have been represented at recent Liege games, and also watched the duo play for Belgium in a friendly international against Luxembourg last week.
Defour, 20, and Witsel, 19, are the two brightest talents in Belgium.
Defour is already club captain and has run up 16 Belgian caps, while Witsel was representing his country for the fifth time in Luxembourg.
If Boro are in a position to harden up their interest in January, it’s more likely that Defour will be the most realistic target.