The 75-year-old led England through the World Cup finals in 2002 and 2006, losing in the quarter-finals on both occasions.
In February last year, Eriksson stepped down from his role at Swedish club Karlstad due to "health issues".
"Everyone can see that I have a disease that's not good, and everyone supposes that it's cancer, and it is. But I have to fight it as long as possible," Eriksson said in an appearance on Swedish Radio P1.
"I know that in the best case it's about a year, in the worst case even less," he said, according to a transcript on P1's website. "I don't think the doctors I have can be totally sure, they can't put a day on it."
Eriksson said he was trying not to think about his illness, adding: "You have to trick your brain. I could go around thinking about that all the time and sit at home and be miserable and think I'm unlucky and so on.
"It's easy to end up in that position. But no, see the positive sides of things and don't bury yourself in setbacks, because this is the biggest setback of them all of course. It just came from nothing. And that makes you shocked," he added.
"I'm not in any major pain. But I've been diagnosed with a disease that you can slow down but you cannot operate. So it is what it is."
Eriksson began his career at Sweden's Degerfors IF, before taking charge of Benfica for an immensely successful spell between 1982-84.
He also won titles at AS Roma, Sampdoria and Lazio before becoming England's first foreign coach in 2001.
Despite only losing five competitive games, Eriksson's time at England was a rollercoaster ride, with some superb performances on the field accompanied by scandals off the pitch.
His England team was billed as a golden generation, with a team comprised of high-profile players like David Beckham, Steven Gerrard, Frank Lampard and Wayne Rooney, but failed to win any major silverware.
Aside from their two World Cup quarter-finals, England also made it to the last eight of the European Championships in 2004, where they lost on penalties to Portugal.
The Swede occupied the front pages following an affair with former FA secretary Faria Alam and was caught in the infamous "Fake Sheikh" sting when a tabloid paper set up him up with a reporter posing as a rich Arab investor.
Following his departure from England in 2006, Eriksson coached a string of teams including Manchester City, Mexico's national team and Leicester City.
His last coaching role of a glittering managerial career that spanned four decades was with the Philippines in 2019.
