O'Brien also teased the possibility of playing one game at Gillette Stadium, the home field of the New England Patriots.
"You give them two yards of plus-yardage, and they get their head of steam going, and that makes an effective running back."
Castro-Fields played five years with the Nittany Lions before being drafted by the 49ers in 2022.
Franklin would be the third coach in school history to win the award.
Ross, who has one year of eligibility left, totaled 129 catches, 1,618 yards, and 14 touchdowns across three seasons with Troy.
Saquon Barkley needs 268 rushing yards over the next two games to break the NFL single-season rushing record.