Hall of Famer Dikembe Mutombo is undergoing treatment for a brain tumour, the NBA has announced.

An eight-time NBA All-Star, Mutombo is regarded as one of the best defensive players in history and sits second in the league's all-time charts for blocks, behind only Hakeem Olajuwon.

Mutombo also won the NBA's Defensive Player of the Year award on four occasions. He retired from playing in 2009 and has turned his focus to humanitarian work.

On Saturday, a statement issued by the league on behalf of Mutombo and his family confirmed the 56-year-old's condition, adding that the former Atlanta Hawks and Denver Nuggets center was in "great spirits".

"NBA global ambassador and Basketball Hall of Famer Dikembe Mutombo is currently undergoing treatment for a brain tumour," the statement read.

"He is receiving the best care possible from a collaborative team of specialists in Atlanta and is in great spirits as he begins treatment.

"Dikembe and his family ask for privacy during this time so they can focus on his care. They are grateful for your prayers and good wishes."

Mutombo also played for the Philadelphia 76ers, New Jersey Nets, New York Knicks and Houston Rockets in his celebrated career.