The 26-year-old centre forward joined Hull City on a free transfer from Portuguese outfit Vitoria Guimaraes on a three-year deal last summer.
Estupinan scored 13 times in 35 games for the Tigers, but his season ended prematurely in March due to an injury.
The Colombian’s performances last season impressed several clubs and he is now attracting interest from several Spanish outfits, according to Argentine journalist Cesar Luis Merlo.
La Liga outfit Granada and Spanish second division outfit Real Valladolid are particularly interested in Estupinan.
And it is suggested that a loan deal with an option or obligation to buy could be the transfer formula to convince Hull City to let the player go.
Estupinan has featured four times for Hull City this season and scored a goal in their defeat against Doncaster Rovers in the EFL Cup.
Hull City have brought two forwards this summer in the form of Lian Delap and Aaron Connolly, and it remains to be seen whether Liam Rosenior’s side will dig in the market to find a replacement if Estupinan leaves.
