The preliminary investigation found the security guard was attacked in the neck while in the crowd of fans, reported Finner during a press conference.
While police are yet to conduct an interview, Finner said medical staff that treated him said he was administered Narcan, a drug used to revive people who have overdosed on opioids. The medical staff observed a needle mark on the neck of the security guard during this assessment.
Narcan was also used to revive other concertgoers as well, but Finner was unable to say how many were attacked.
"We do know that there were several, many, instances where they did administer Narcan on site," he said.
Meanwhile, the mayor of Houston will "leave no stone unturned" as he investigates the Astroworld Festival tragedy.
Sylvester Turner has promised to launch a "thorough review and investigation" of the crowd surge at the music festival in Texas, which caused the deaths of at least eight people.
He told CNN: "We're not going to leave any stone unturned. We want to look at every single detail to determine what led up to it and what additional steps that need to take place to keep it from happening again, especially in this city."
He told the New York Times newspaper: "We had more security over there than we had at the [baseball] World Series games ... we are looking at all potential causes of this incident or what caused the cardiac arrest. We're not taking anything off the table."
Travis Scott was performing at the festival when the crowd surge occurred.
The rap star stopped his performance and called for urgent help, as the seriousness of the situation became apparent.
Travis said at the time: "Security, somebody help real quick."
