The get-togethers were part of a series of meetings the presumptive Democratic nominee held on Friday to discuss the selection of her potential running mate. She is expected to make an announcement sometime next week.
Warren and Castro are both being vetted by the campaign for the spot.
According to sources, Clinton has not yet selected her running mate; however, she is closing in on making that decision.
His office told ABC News he was not invited, nor was he planning, to meet with Clinton today.
ABC News' Ali Rogin contributed to this report.