Barkley will reveal whether he's decided to stay at USC or enter the NFL draft at a news conference at 4 p.m. ET in Heritage Hall.
Will he be like Matt Leinart, who stayed, or Mark Sanchez, who bolted for the NFL?
USC already has lost defensive end Nick Perry and offensive tackle Matt Kalil early to the NFL draft, but if Barkley opted to return, the Trojans would likely start the season ranked in the preseason top 10, perhaps top 5.
Said McDonald in a statement: "Being a captain of this team and part of that greatness, we have an opportunity to do something great. That opportunity doesn't come around very often. I want to finish things out and be a part of something great. So I am returning to USC for my senior season."
McDonald was named a first-team All-American by both the Sporting News and Pro Football Weekly and also was named first-team All-Pac-12 conference. McDonald finished third on the team in tackles (67) and also added three interceptions as the Trojans finished the season with a 10-2 record.