Representatives for Douglas have confirmed to ABCNews.com that doctors discovered a tumor in the Oscar-winning actor's throat.
The Oscar-winning actor's spokesperson told People magazine Monday that doctors expect him to "make a full recovery."
"I am very optimistic," Douglas said in a statement.
Representatives for Douglas declined ABCNews.com's requests for further comment.
The news comes ahead of the premiere of Douglas' latest movie, "Wall Street: Money Never Sleeps," due to open in theaters Sept. 24. It's unclear whether his treatment will affect the promotion of the highly anticipated follow-up to 1987's "Wall Street."
The 65-year-old actor and husband of actress Catherine Zeta-Jones has had a harrowing year.
"I've had a rough year on the personal front," he told the Chicago Sun-Times in June. "It's been pretty well publicized."'
In April, his son, Cameron Douglas, was sentenced to five years in prison on drug charges. In a bid to keep Cameron from a long stint in jail, Douglas hand-wrote an impassioned, five-page letter to Manhattan federal judge Richard Berman, referring to his family's history of drug abuse.
"Dear Judge Berman," he wrote, "I don't want to burden you with a litany of my son, Cameron's rehab history, beginning at 13. He's an adult and responsible for his own life. We do know, however, that genes, family, and peer pressure are all a strong influence on a substance abuser."
Michael Douglas suggested that his family's fame -- he is the son of Kirk Douglas, one of Hollywood's biggest stars in the 1950s and '60s -- could be to blame for his son's dependence on drugs.
"I have some idea of the pressure of finding your own identity with a famous father," he wrote. "I'm not sure I can comprehend it with two generations to deal with."
Douglas told the Sun-Times that when he first became a father, the travel involved with making movies forced him to be away from Cameron. He said he doesn't want to make the same mistake with his children with Zeta-Jones, Dylan, 10 and Carys, 7.
"My priorities have completely changed. My marriage and my families come certainly before my career," he said."I cherish the time with them. I'm picking a lot fewer projects now. It's tough to get me out of the house."