The Portuguese outlet Bola state that Gundogan spent three days in Barcelona and that the nature of his visit is unknown.
Bola has gone onto state that the visit has sparked speculation regarding the Germany international’s future.
Barcelona were closely linked with a move to Barcelona last season but was unable to agree personal terms with the Catalan giants.
Gundogan will miss Euro 2016 after dislocating his knee during training earlier this month. The German tabloid Bild report that it will take Gundogan four to six months for him to make a full recovery.
The 25-year-old has seven assists and three goals in 40 appearances for Dortmund this season.