Bob Gunnell said in a statement that Ali's condition was fair, a brief hospital stay was expected.
RNZI reports former heavyweight world champion Ali, 74, has been suffering from Parkinson's disease for more than three decades.
Ali, who lives in Phoenix, Arizona, has suffered some health problems in recent years.
He was admitted to hospital in December 2014 with what was believed to be a mild case of pneumonia.
Doctors later determined he was actually suffering from a severe urinary tract infection, for which he received further treatment in hospital in January 2015.
In recent years, he has kept a low profile and his last public appearance was in April at the 'Celebrity Fight Night' gala in Arizona, a charity that benefits the Muhammad Ali Parkinson Centre.
Nicknamed the greatest, he retired from boxing in 1981 with a 56-5 record