According to the Dallas Police Department, officers were dispatched to the bar around 9:40 p.m. A 30-year-old man said he was physically assaulted but could not identify who assaulted him. The man was taken to the hospital with non-life-threatening injuries.
A Dallas Police spokesperson said no arrests or suspects have been reported in connection with the incident, which was first reported by 105.3 FM The Fan in Dallas. The investigation is ongoing, according to police.
An NFL official said the league is aware of the situation involving Elliott and "looking into it to understand the facts."
Elliott is already under NFL investigation stemming from a 2016 domestic violence accusation against him. The running back had been preparing a response to the league to be submitted in the next week, sources told Schefter.
Multiple sources told Schefter that Elliott could face a one- or two-game suspension, but the NFL has denied that any decision on discipline has been made and said it could not be made until its investigation is complete.
On Saturday, Elliott was the star of the National Fantasy Football Convention at Fair Park in Dallas. He signed autographs and greeted fans. He even jumped in the Salvation Army red kettle that was on hand to re-create his celebration after a touchdown against the Tampa Bay Buccaneers last season.
He also took part in a charitable event with Operation Homefront that gave a house to a woman in the armed forces.
But Sunday's incident adds to the series of off-field issues involving Elliott since his first NFL season.
In August, before his first preseason game against the Seahawks, Elliott was spotted at a marijuana dispensary in Seattle. Owner and general manager Jerry Jones was not pleased.
"In general, while it may not be wrong, it's just not good," Jones said of Elliott's visit. "I don't want to say anymore."
Elliott found himself interacting with police at a bar in February, when he spoke with officers who were arresting a friend of the Cowboys player, according to TMZ. Elliott was not accused of any wrongdoing.
In March, Elliott was seen in a video exposing a woman's breast from the rooftop of a Dallas bar during a St. Patrick's Day parade.
Returning from a charity event in May, Elliott was the passenger in a car crash. He missed some time during organized team activities because of general soreness but was able to do everything else for the rest of the offseason.
During the June minicamp, Elliott spoke about slowing down off the field.
"Just trying to learn to stay out of the way," Elliott said. "Whatever you do is going to be seen."
Elliott is accustomed to the spotlight since his playing days at Ohio State, but he said the intensity has been greater with the Cowboys. He said he learned lessons from his missteps as a rookie as well as this offseason.
"I think it's just life," Elliott said in June. "You learn from your mistakes, and if you don't, it can be brutal. So it's just part of life."
The Cowboys have had a number of off-field problems this offseason. Defensive end David Irving was suspended for the first four games of the 2017 season for violating the NFL's policy on performance-enhancing drugs.
Cornerback Nolan Carroll was arrested in late May for suspicion of driving while intoxicated after a party in the Uptown section of Dallas. Linebacker Damien Wilson was charged with two counts of aggravated assault with a deadly weapon on July 4.
Both players are subject to NFL penalties under the substance abuse and personal conduct policies whether they are legally found in the wrong or not.
ESPN's Todd Archer contributed to this report.