San Francisco offensive lineman Thomas Herrion collapsed in the locker room and died Sunday morning, shortly after the 49ers played the Denver Broncos in a preseason game. He was 23. Herrion, a 6-foot-3, 310-pound guard, was on the field for San Francisco's 14-play, 91-yard drive that ended with a touchdown with 2 seconds left. Players had finished listening to coach Mike Nolan address them in a postgame meeting when Herrion collapsed. Medics administered CPR on him and took him to an ambulance that rushed him to a nearby hospital. About three hours later, 49ers spokesman Aaron Salkin confirmed that Herrion had been pronounced dead. The cause of death was not immediately known. The San Francisco Chronicle reported that television footage showed Herrion walking off the field after the 49ers' touchdown drive, with nothing apparently wrong. According to the paper, Herrion's face gave no sign of distress in the footage. "This is a colossal tragedy for the 49ers and the entire NFL community," Salkin said. "We still do not know all the details. Our thoughts and prayers are with the Herrion family."