Noel was not available to comment.
The Sixers will play their second consecutive season without a franchise center if Noel can't go. Andrew Bynum missed last season with chronically injured knees before he signed with the Cavaliers last summer.
But Noel's situation is different.
The Sixers acquired him from New Orleans in a draft-day trade for all-star point guard Jrue Holiday. At the time, Noel was expected to be sidelined until December while he recovered from the injury, suffered in February during his lone season at Kentucky.
Bynum's knees are deteriorating, but Noel is expected to make a full recovery. He underwent surgery in March.
Noel, 19, spent 51/2 months rehabilitating in Birmingham, Ala., with physical therapist Kevin Wilk and his staff before moving to Philadelphia last month.
In mid-September there were doubts that Noel would be ready to play by December because he was not in basketball shape. Two weeks ago, Brown said there was no timetable for the center.
Noel has spent this preseason traveling with the Sixers and performing post-practice shooting drills with Brown and big-man coach Greg Foster after practice.
"He can focus on his game and focus on getting back into the weight room and focus on getting himself better and getting back to 100 percent, and just being ready for next year," forward Thaddeus Young said. "Only he's going to know how he is going to feel and how he does feel."
Brown added: "He needs to be nurtured this year. We have an opportunity."
Although Noel is not playing, the Sixers want him to get an up-close look at life in the NBA.
"I like the fact that he is with us every single day and every single way," Brown said. "He's in video sessions, practice, shootarounds. It's a classroom. It's an opportunity for him to learn from me and the NBA. And we don't want to waste this year."
Noel was a candidate for the first overall draft pick but slipped to sixth after he was hurt. Before the injury, Noel had an outstanding campaign at Kentucky, averaging 10.5 points, 9.5 rebounds, and 4.4 blocked shots, and making 59 percent of his shots from the field. He had a school-record 12 blocked shots against Mississippi last season.
"My advice to him is don't rush," said Sixers guard Tony Wroten, who suffered the same injury as a junior in high school. "I know he wants to play. He's never been on an NBA court . . . but he's got to wait till the time is right. It's an ACL, not a sprained ankle. It's the real deal."