ST. PAUL — Minnesota’s governor says he suffered lung damage while recovering from back surgery, keeping him at the Mayo Clinic for more than a month.

Gov. Mark Dayton underwent two spinal fusion surgeries last month to improve his leg strength and had been expected to be released from the hospital within days. His office gave no formal update on his status until this week, when a Dayton spokeswoman confirmed he remained at the hospital for what was described as “physical therapy.”

The 71-year-old governor said in a statement emailed Thursday that post-surgical complications had damaged his lungs, providing no other details. Dayton said he had stayed at the Mayo Clinic to treat his lungs on his doctor’s recommendation. He said he expected to be released “in the next few days.”

Dayton said he’s been in constant contact with commissioners and staff.

The Democratic governor hasn’t been seen publicly since before his first surgery, performed on Oct. 12. His office did not immediately respond to questions seeking more detail on his health.

Dayton’s two terms in office have been marked by recurring health problems. He had already undergone three similar back surgeries and a separate procedure to repair a torn hip muscle.

Last year, Dayton revealed he had been diagnosed with prostate cancer one day after collapsing during his State of the State address. Dayton had surgery and is now in remission.

Dayton didn’t seek a third term . He’ll leave office Jan. 8.