Kentucky doctor pleads not guilty to assault of Sen. Rand Paul

— -- The Kentucky doctor who allegedly attacked Sen. Rand Paul, leaving him with six broken ribs, pleaded not guilty to fourth-degree assault charges Thursday.

Rene Boucher, 59, Paul's next-door neighbor for 17 years, tackled the senator to the ground last Friday, according to his arrest warrant. As Paul is a member of Congress, U.S. Capitol Police and the FBI assisted in the investigation of the incident.

Paul tweeted about his injuries Wednesday, sharing the news about his broken ribs and adding that he had a pleural effusion, which is an accumulation of fluid resulting from inflammation or changes in pressure in the chest.

The senator additionally appeared to hint at his side of the incident Wednesday, retweeting news stories that pushed back on earlier reports that the alleged assault was the result of a dispute over landscaping.

Boucher's attorney claimed Thursday in an interview with ABC News that the incident did, in fact, start as a landscaping dispute and that Paul was not "blindsided" by his client. He added that claims the encounter was politically motivated were incorrect and that he received a letter from the senator's attorney that Paul intends to sue.

On Monday, a statement from the attorney claimed that the incident was spurred by a "trivial" dispute.

"We sincerely hope that Sen. Paul is doing well and that these two gentlemen can get back to being neighbors as quickly as possible," reads the statement.

ABC News' Ali Rogin and Mariam Khan contributed to this report.