Story highlights Sen. Rand Paul suffered six broken ribs after an alleged attack

His neighbor pleaded not guilty to misdemeanor assault charges

Washington (CNN) Sen. Rand Paul returned to the Senate on Monday after being seriously injured at his home in an alleged attack by his neighbor earlier this month.

There was "no justification" for his being attacked 10 days ago while doing yard work at his home in Kentucky, Paul told the Washington Examiner in his first interview since the incident.

The report said the senator was struggling to breathe and often stopped to catch his breath and talk. Paul also said he knew of no motive that would have sparked his neighbor to hit him from behind.

"From my perspective, I'm not really too concerned about what someone's motive is. I'm just concerned that I was attacked from the back and somebody broke six of my ribs and gave me a damaged lung where at least for now I have trouble speaking and breathing and now I've hurt for 10 days," Paul said.

Paul returned to the Senate Monday afternoon as Republicans began marking up their tax plan in the finance committee.