"We completely support the decision each young man made during the spring and summer as they evaluated their personal circumstances," coach Pat Fitzgerald said. "All four Wildcats have been outstanding teammates throughout their time in our program. Nothing about the support we promised their families during recruitment will waver, with the full complement of scholarship, academic, sports medicine and professional development resources available."
Whillock was one of the leading tacklers returning for Northwestern on defense with 78 tackles, three tackles for loss and two fumble recoveries last season. Miller was projected as a starter along the defensive line and had 29 total tackles with 2.5 tackles for loss last season.
The Wildcats have depth at quarterback despite Smith, who was not projected to start, deciding to opt out. They have Indiana grad transfer Peyton Ramsey, previous Clemson transfer Hunter Johnson and junior Andrew Marty, among others.
Northwestern also had offensive tackle Rashawn Slater, a starter, opt out of the season and declare for the NFL draft in August.
Miller, Smith, Whillock and Whittaker all made the decision to opt out before training camp opened last month, a source told ESPN's Adam Rittenberg. There's a chance some of the players would return in 2021.