Armando Salguero of the Miami Herald noted McMillan was removed from the game with the knee injury. Later in the game, Andy Slater of 940 AM in Miami reported the Dolphins fear McMillan suffered a torn ACL.
McMillan, 20, was selected by the Dolphins with the No. 54 overall pick in this year's draft. With Koa Misi's offseason spinal fusion surgery, McMillan came into the season with an excellent chance to earn a starting position next to Lawrence Timmons and Kiko Alonso.
Given that Timmons traditionally plays inside linebacker, however, McMillan has had to adjust to taking reps on the outside, as opposed to his more familiar position on the inside.
At Ohio State, McMillan was a tackling machine, accumulating 221 combined in his sophomore and junior seasons. He's shown solid instincts and the ability to play downhill, though his skill set suggested a move to outside linebacker in the NFL was likely.
Because both Timmons and McMillan have positional versatility, however, Dolphins defensive coordinator Matt Burke has the option to utilize both in various schemes and roles. That makes McMillan's injury a potentially major blow for the Dolphins.
With McMillan injured, Neville Hewitt or Mike Hull will likely take his place.