The 79-year-old musician, who is expected to make a full recovery, joined the rock band in late 1962.
He left in 1993, but is still musically active, releasing a solo album, Back To Basics, last year.
A spokesman said: "He is undergoing treatment and is expected to make a full recovery, as it was caught in the early stages.
"The Wyman family has asked for their privacy during this time."