"Thanks @NDFootball and @CoachBrianKelly for everything," Russell wrote on Twitter. "I'm leaving, but grateful for my time at @NotreDame."
Although he was honored by the Fighting Irish on senior day, Russell had the opportunity to ask the NCAA to grant him a fifth year. He missed the entirety of the 2014 season after getting into academic trouble.
As Irish Illustrated's Pete Sampson noted, Notre Dame has lost a trio of key players in the matter of a few days:
In 11 games in 2015, Russell recorded 60 total tackles, 3.5 tackles for loss and two interceptions.
He isn't widely considered the best cornerback in the 2016 draft class, but he's likely to be a second- or potentially first-round selection. In his most recent big board, Bleacher Report's Matt Miller listed Russell as the 88th-best player overall and the No. 8 cornerback. Miller does, however, consider the Notre Dame star the "biggest question mark" at his position.
Russell's stock will likely start rising once the draft process begins as long as he shows he has fully recovered from his tibia injury.
His departure will leave the Fighting Irish somewhat thin at corner next season. According to Mike Vorel of the South Bend Tribune, they'll have only three players who've started a game:
Notre Dame's defense as a whole could be decimated by graduation and early draft entry. Leading tackler Jaylon Smith could be on his way out. His knee injury suffered in the Fiesta Bowl might change those plans, though. Joe Schmidt, who finished second in tackles, is graduating, and the duo of Romeo Okwara and Sheldon Day, the team's top two sack leaders, are both seniors.
Russell's decision to enter the NFL draft won't come as a surprise for head coach Brian Kelly, but it still forces the Fighting Irish to replace their best cornerback from the past year.