CHICAGO -- A man who was traveling on United Airlines flight 3411 from Chicago to Louisville was forcibly removed when the flight was oversold Sunday night.

The Chicago to Louisville flight was oversold and several passengers were chosen at random to be bumped from the flight, including the man and his wife.

Passenger Jayse Anspach, who tweeted video of the incident, said that security pulled the man, who says he’s a doctor, from his chair after he refused to leave the aircraft.

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“The doctor needed to work at the hospital the next day, so he refused to ‘volunteer,’ United decided to use force on doctor,” said Anspach.

@United overbook #flight3411 and decided to force random passengers off the plane. Here's how they did it: pic.twitter.com/QfefM8X2cW — Jayse D. Anspach (@JayseDavid) April 10, 2017

As security pulled the man from his seat, Anspach said, “the doctor’s face was slammed against an arm rest, causing serious bleeding from his mouth.” The security detail then dragged the man off the aircraft.

“That officer has been placed on leave effective today pending a thorough review of the situation,” the department said in a statement, CBS News transportation correspondent Kris Van Cleave reports.

Oscar Munoz, CEO of United Airlines, said it was “an upsetting event to all of us here at United.”

“I apologize for having to re-accommodate these customers,” he said.

“Our team is moving with a sense of urgency to work with the authorities and conduct our own detailed review of what happened. We are also reaching out to this passenger to talk directly to him and further address and resolve this situation.”

United CEO response to United Express Flight 3411. pic.twitter.com/rF5gNIvVd0 — United (@united) April 10, 2017

In an email sent to United employees late Monday -- and obtained by CBS News -- Munoz said he believes “there are lessons we can learn from this experience.”

“Treating our customers and each other with respect and dignity is at the core of who we are, and we must always remember this no matter how challenging the situation,” Munoz wrote.

Munoz also showed support to his employees.

“While I deeply regret this situation arose, I also emphatically stand behind all of you, and I want to commend you for continuing to go above and beyond to ensure we fly right,” he wrote.

Munoz shed light on the incident in the email to employees with a play-by-play account of how everything unfolded: