(CNN) Democratic presidential front-runner Joe Biden says he has informed his Democratic rival for the nomination, Vermont Sen. Bernie Sanders, that he is beginning the process of vetting potential vice presidential running mates.

"I am in the process and I've actually had this discussion with Bernie because he's a friend -- we're competitors, he's a friend," the former vice president told donors during a virtual fundraiser on Friday.

Biden, who currently holds a sizable delegate lead over Sanders in the nomination fight, said he doesn't want the Vermont senator to "think I'm being presumptuous."

"But you have to start now deciding who you're going to have background checks done on as vice presidential candidates and it takes time," he added.

Read More