The hospital said that the 54-year-old country singer was taken into surgery to relieve pressure on his brain, despite earlier reports that he had "shown signs of improvement."
"He is in critical condition," his publicist said. "We will have updates as they become available. His family and friends here with him at the hospital request your prayers and support."
Travis, who has sold more than 25 million records and won numerous awards during his decades-long career, was admitted to the hospital on Sunday with viral cardiomyopathy -- a condition that weakens and enlarges the heart muscles.
2014: The Year in Music [PHOTOS]