Noel tore his ACL on Tuesday night when No. 25 Kentucky lost at Florida. An MRI revealed the injury, and the 6-foot-10 forward will have surgery in the next two or three weeks.
The projected recovery period is six to eight months.
Noel's injury deals a serious postseason blow for the defending national champions, who had appeared to be gaining some footing after struggling earlier this season while trying to blend in four freshmen. Leading the way defensively for the Wildcats was Noel, who began Tuesday first in the nation with 4.5 blocks per game.
The rookie took a positive approach to the diagnosis, posting on Twitter, "Minor setback for a MAJOR comeback! I love you all and can't thank y'all enough for the prayers."
Noel was hurt with 8 minutes left in the Wildcats' 69-52 loss to the seventh-ranked Gators. He ran into the basket support after blocking a layup from behind. Noel landed awkwardly, dropped to the floor and started screaming while clutching his knee.
Noel had eight points, six rebounds and three blocks before the injury.
"I've been coaching for 22 years and this is the first injury we've had of this kind during the season, which makes it even more devastating," Kentucky coach John Calipari said in a statement.
"I met with Nerlens earlier today. The meeting was really positive, and I loved his attitude. The way he is already dealing with this injury lets me know that he is going to come back stronger than ever. ... Obviously this is not a career-ending injury and it's one that athletes bounce back from all the time."
The question is if Kentucky (17-7, 8-3 Southeastern Conference) can bounce back from the devastating loss.
With Noel out, 7-footer Willie Cauley-Stein now must man the post for Kentucky after spending most of the season as Noel's backup. Cauley-Stein missed four games last month after having a procedure on his left knee, an absence that meant even more minutes for Noel.
The Everett, Mass., native clearly relished the extra work, which gave him a chance to display an array of skills. Besides his shot-blocking prowess, Noel was averaging 10.6 points, 9.5 rebounds and 2.1 steals per game, with the latter two statistics both ranking 26th nationally.
He entered the game with three consecutive double-doubles and on a four-week run as the conference's top freshman. In his previous five games, Noel had blocked 26 shots.
While Kentucky has lacked a bona fide team leader, there was no doubt that the Wildcats seemed to feed off of Noel's intensity and athleticism. Calipari's wish has been for other players to display those some traits.
Now, the Wildcats have to rework the rotation without their biggest star. Kentucky's tallest player besides Cauley-Stein is 6-10 sophomore Kyle Wiltjer, whose game had recently blossomed along with Noel's.
Former Wildcats center Sam Bowie believes the injury might initially affect the team's psyche, especially with so many young players.
"His teammates will start to second-guess themselves, and that's just human nature," Bowie said. "You always say, `We'll regroup; people have to step up and take their games to another level,' and that's been the politically correct thing to say, but realistically speaking it will affect the team mentally."
Considered the nation's top recruit last season, Noel led a four-man freshman class also including Archie Goodwin and Alex Poythress that was expected to pick up where last year's championship team left off. Noel has often been compared to national player of the year Anthony Davis because of his size and shot-blocking ability.
While Noel downplayed the comparison, he made clear his pursuit of breaking Davis' single-season school record of 186 blocks set last year. A Kentucky-record 12 blocks during an 87-74 victory at Mississippi on Jan. 29 put him slightly ahead of Davis' pace, which was set over 40 games.
More importantly, Kentucky's victory over the then-No. 16 Rebels helped re-establish its credentials as an NCAA tournament team. Their first win over a ranked opponent was part of a season-best five-game winning streak that helped put the Wildcats back in the Top 25 on Monday for the first time since falling out Dec. 3 following consecutive losses to Notre Dame and Baylor.
Tuesday's game against Florida was supposed to be another big test, but Kentucky trailed by as many as 19 points before Noel's injury. The Wildcats seemed even more shaken afterward, and their winning streak vanished.
Kentucky visits Tennessee on Saturday before returning home Wednesday against Vanderbilt, providing the Wildcats chances to sweep season series against both schools and stay in the SEC race.
Bowie believes Calipari is capable of motivating the Wildcats to overcome Noel's absence, band together as a team and return to the postseason - suggesting that urgency sometimes brings out the best performances.
"I still feel like they'll make the tournament," Bowie said, "but whether they have a legitimate chance of making a serious run, that will be determined. With Cal as coach, and I think they have plenty of personnel, they have a chance to be one of the 65 teams invited to the tournament."