Noel, a 6-foot-10 forward, played 24 games for Kentucky before he suffered a torn anterior cruciate ligament in his left knee. He averaged 10.5 points and led the SEC with 9.5 rebounds a game. His average of 4.4 blocks a game was the best in the country.
"I have loved my time at Kentucky but I feel that I'm ready to take the next step to the NBA," Noel said. "I've learned so much here at UK and am thankful for Coach (John) Calipari, the staff and my teammates for all of their support.
"I especially appreciate the Big Blue Nation and all of the support, prayers and well-wishes I've received from them during my rehab and decision-making process. I'll always be a Wildcat!"
Calipari said he supported Noel's decision t leave school.
"The hard work and will to win he showed on the floor this year and the dedication and attitude he has shown in his rehab will only be a reward for him and whatever team drafts him in June," Calipari said.
Kentucky, which won the 2012 NCAA Tournament but didn't earn a berth in 2013, has lost several high-profile freshmen to the NBA in recent years. John Wall was the No. 1 overall pick in 2010 and Anthony Davis went first last year. Noel is considered a possible No. 1 selection.