Barcelona were reportedly interested in signing Dembele last summer when he opted to leave French side Rennes for Dortmund instead.
The 20-year-old has been an instant hit in Germany, scoring 10 goals and providing 21 assists in his 49 appearances for the Bundesliga giants.
And Dembele's French colleague Umtiti, who arrived at the Nou Camp from Lyon last summer, has revealed Barca remain keen on signing the winger.
But Umtiti admits nothing is official yet.
Barcelona are interested in signing Borussia Dortmund winger Ousmane Dembele
Barcelona are interested in Borussia Dortmund's Ousmane Dembele
"We get on really well,” Umtiti told L’Equipe when asked about Dembele.
“I know Barca are interested in his profile, but all the parties need to reach an agreement.
"Dembele would do well with us, with the quality he has he's capable of adding a lot.
Samuel Umtiti plays with Ousmane Dembele in France national side New Barcelona kit revealed for 2017/18 Mon, May 29, 2017
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“If he comes he will be welcome, but it still needs to be official to talk about that. If he comes, he can sleep at my house!"
Dembele won the German Cup in his first season at Dortmund, who paid £13million for the Frenchman, and helped them to a third place finish in the Bundesliga.
Umtiti also enjoyed an impressive maiden season at the Nou Camp, helping Barcelona to the Copa del Rey and Spanish Super Cup.