Fabregas joined Barca from Arsenal last summer and despite starting impressively at Camp Nou, lost form in the second half of the campaign.
The arrival of Alex Song from Arsenal this summer has raised doubts on whether Fabregas will play regularly for the Blaugrana, but Xavi has faith in the 25-year-old.
"Cesc is important for the team," he told AS.
"He will make a difference over the course of the season and score some vital goals."
Barcelona have won all three of their La Liga games so far.