US senator Rand Paul suffered serious injuries during an assault at his Kentucky home, it has emerged.
He is said to be recovering from five broken ribs and bruises to his lungs. A spokesman said the Republican senator is in "considerable" pain.
Initial reports had suggested that Mr Paul's injuries were only minor.
He was assaulted at his gated community home in Bowling Green, Kentucky, on Friday, allegedly by a neighbour who has since been charged with assault.
"Senator Paul has five rib fractures including three displaced fractures," Doug Stafford, a senior adviser to Mr Paul, said in a statement reported by US media.
"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."
Mr Paul was mowing his lawn at the time of the attack, reports WAVE-TV, a Kentucky television station.
The Republican "was blindsided and the victim of an assault" on Friday, a spokeswoman for him was quoted by US media as saying.
On Sunday, the senator tweeted that his wife "Kelley and I appreciate the overwhelming support after Friday's unfortunate event. Thank you for your thoughts and prayers."
Rene Boucher, 59, has been charged with fourth-degree assault, police say.
The two had a previous disagreement about a property line involving a creek behind the senator's house, NBC News reports.
Matthew Baker, a lawyer for Dr Boucher, said in a statement that the dispute was "trivial".
"Senator Paul and Dr Boucher have been next door neighbours for 17 years," said the attorney.
"They are also prominent members of the local medical community and worked together when they were both practising physicians.
"The unfortunate occurrence of November 3rd has nothing to do with either's politics or political agendas.
"It was a very regrettable dispute between two neighbours over a matter that most would regard as trivial."
Mr Paul, seen as representing the libertarian wing of the Republicans, ran for the party's presidential nomination in the 2016 election, but dropped out after a fifth place finish in the Iowa caucuses.
An ophthalmologist, he represents Kentucky in the US Senate and is the son of former Congressman Ron Paul, who ran for president several times.