Hull and Brighton have the strongest interest in the winger, with Brentford also monitoring his progress.
Santos plays for Dutch side NEC, who sit in sixth place in the Eredivisie.
The 27-year-old holds a German passport, and so crucially will not be subject to a work permit.
He has scored 11 goals in 17 league games this season, and a further two in three matches in cup competition.
His form has led to an international call up for Venezuela, for who he has four caps, and netted for his country against Brazil in October.
Last season he netted an impressive 23 goals, showing his displays in 2015/16 are no flash in the pan.
For promotion chasing sides like Hull and Brighton, adding Santos could make a major difference if he can settle quickly to life in the Championship.