The 24-year-old has established himself as one of the best centre-backs in European football over the past three seasons, during which he helped Jurgen Klopp's side win successive Bundesliga titles in 2011 and 2012.
"My father and I reject 99.9% of the teams, from all over the world, when they come to us," Hummels told Bild.
"But Barcelona is one of two or three clubs who I would consider maybe signing for. I would study it to see if it made sense to leave. I am not saying I want to go."
Hummels's current contract with Dortmund runs out in June 2017.