Williams indicated the combination of McDonald not be fully healed and not wanting to lose the majority of a season factored into his decision.
"He couldn't play in a game today and this is Jan. 13," Williams said. "So he couldn't play in a game today, so you're talking about the limited access he would have to play the rest of the season. He feels comfortable but I would say not 100 percent confident about all of his moves and everything right now. He's getting better every day... Deep down, it's the smartest thing to do."
While Williams suggested that team doctors might say that McDonald is a month ahead of schedule, the junior guard is not ready to defend in a game situation.
Harrison Barnes told reporters that it was clear in practice that McDonald isn't quite ready to return.
"The biggest thing is he's actually out there playing offense and playing defense now," Barnes said. "First it was getting him out there first for form shots and then doing light little jogs up and down, but now it's nice to see that he can run up and down the court two or three times without his knee bothering him, playing offense, playing defense, so that's good."
McDonald tore the anterior cruciate ligament in his right knee on July 14 during a N.C. Pro-Am summer league game at the McLendon-McDougald Gymnasium on N.C. Central University's campus in Durham. Team orthopaedist Dr. Alex Creighton performed McDonald's surgery at UNC Hospitals on Aug. 3. At the time of the surgery, the estimated recovery time was set at 7-8 months.
McDonald averaged 7.0 points per game in 2010-11 and ranked second on the team with 51 made 3-pointers.
UNC tweeted that McDonald would apply for a medical red-shirt following the season, which is relevant only if he suffers another injury or setback in one of his final two seasons of eligibility and intends to request a sixth year.