BOWLING GREEN, Ky. — Sen. Rand Paul is recovering from five broken ribs and bruises to his lungs, and it is unclear when he will return to Washington, aides said Sunday, signaling that injuries he sustained Friday are far more severe than initially thought.

The second-term Republican senator from Kentucky and 2016 presidential candidate was attacked, allegedly by a next-door neighbor, Rene Boucher, 59, who was charged with fourth-degree assault.

Paul made his first public comments since the incident on Sunday, tweeting that his wife “Kelley and I appreciate the overwhelming support after Friday’s unfortunate event. Thank you for your thoughts and prayers.”

Doug Stafford, Paul’s chief of staff, said in a statement Sunday that the senator has five rib fractures, including three displaced fractures, meaning the bones are partly or completely cracked.

“This type of injury is caused by high velocity severe force. It is not clear exactly how soon he will return to work, as the pain is considerable as is the difficulty in getting around, including flying,” Stafford said.

Paul has lung contusions, or bruises, caused by the broken ribs, Stafford said. He could not say whether one lung was bruised or both, but said Paul’s recovery could last several months. Such fractures can cause other significant medical problems, including internal bleeding, damage to other organs or pneumonia.

The nature of the dispute between Paul and Boucher remained a mystery Sunday to locals who know both men as medical professionals based in this southwestern Kentucky town.

Paul is an ophthalmologist who has practiced in town since moving here with his wife in 1993. He continues to provide free medical care to low-income Kentucky residents on a regular basis throughout the year when the Senate is not in session.

Boucher is an anesthesiologist and the inventor of the Therm-a-Vest, a cloth vest partly filled with rice and secured with Velcro straps that is designed to help with back pain. He has worked at several local medical facilities through the years, according to public health records.

David Ciochetty, a doctor with Interventional Pain Specialists in Bowling Green, said in an interview Sunday that Boucher worked there as a “general pain medicine physician” for about a year and a half beginning in January 2010 before leaving.

Asked whether he knew what might cause Boucher to lash out,…