-- The shock and disbelief hadn't worn off Sunday for the San Francisco 49ers as they mourned the death of offensive lineman Thomas Herrion, who collapsed in the team's locker room Saturday night in Denver following an exhibition game against the Broncos.

"It's a day of mourning for the 49er family, as you all know," Mike Nolan, the club's first-year coach, said at a late-afternoon news conference outside the team's training facility. "We lost a teammate and a very good friend as well. . . . Right now we're looking for ways to help our players and coaches, certainly, cope with this tragedy."

The Denver coroner's office performed an autopsy on Herrion, 23, but indicated that no cause of death would be determined until after the results of toxicology tests are available, likely in three to six weeks. Herrion was taken to St. Anthony Central Hospital in Denver and pronounced dead at 11:18 p.m. Mountain time Saturday.

Herrion, a guard listed at 6 feet 3 and 310 pounds on the 49ers' roster, was on the field for the team's 14-play touchdown drive near the end of a 26-21 loss to the Broncos at Invesco Field at Mile High. Club officials said that Herrion took oxygen on the sideline after the drive. But that, they said, was not regarded as unusual following such a lengthy drive in a game played in Denver's high elevation. Herrion did not appear to be in distress as he left the field after the game, in which he played about 20 snaps.

"He looked like regular Thomas," Herrion's agent, Fred Lyles, said in a telephone interview. "And in the plays right before that, if you watched, he was active and strong."

Nolan said that Herrion was "responsive" during and immediately after the game. Herrion spoke to Guy McIntyre, the former 49ers offensive lineman who works in the club's front office, on the sideline. He shook hands with Broncos players, talked to fans as he left the field and joked with the team's nutritionist in the locker room, according to Nolan.

Nolan addressed his players, and then players and coaches said the Lord's Prayer while kneeling.

"Right about the time of completion, someone in the back had said that Thomas was down," Nolan said. "At that time everyone kind of stood up and cleared out. The medical staff immediately came to Thomas, who was at that time laying on the ground."

Said Scott Scharff, a rookie defensive end: "The paramedics came into the locker room and worked on him, and then took him away. . . . Everyone was scared. Anytime you see one of your teammates collapse like that, your heart goes out to him. After that happened, we were just on our knees praying for him that everything would work out."

Gene Upshaw, the executive director of the NFL Players Association, said the research he conducted Sunday indicated that proper emergency procedures had been followed. The league and the union added a requirement two years ago that a trauma physician be at every game, he said.

"That was all in place with this kid," Upshaw said in a telephone interview. "There was nothing anyone could have done that wasn't done. In a matter of minutes, he had the proper medical attention and was at the hospital."

Upshaw said that medical advisers for the league and union told him that those involved in the case had found no evidence of bleeding in Herrion's head or elsewhere.

"They haven't been able to find anything that would explain this," Upshaw said. "It's a person that might have some medical problems that no one knew about or even he didn't know about."

Lyles said: "I talked to people who were in the locker room, and they said the medical people did everything you could humanly do to keep him alive. They treated him very quickly. Of all the places where you could collapse like that, this was where you would want to do it, with all the medical attention so near to you."

Lyles, like Nolan, said he was not aware of any medical condition that could have contributed to Herrion's death.

"I've been the only agent he's ever had, so I would know if something had shown up on a physical," Lyles said. "He had physicals in college. He had physicals in Dallas and San Francisco. He had a physical before he went to Europe and one when he came back. Nothing showed up."

Herrion played in NFL Europe in the spring after spending time on the practice squads of the Dallas Cowboys and 49ers last season. He played in college at Utah after transferring from Kilgore (Tex.) Junior College. He was born in Fort Worth, where his father, who died last year from a stroke, was a minister.

Lyles said that Herrion had worked out on steamy days in Texas in recent months, so he is surprised about speculation that his death might be heat-related. Saturday's game ended with temperatures in the 60s in Denver.

"If there was something wrong with him, you would think it would have shown up when he was working out in that Texas heat," Lyles said.

Lyles said that Herrion was "in that range of 310 to 315 pounds" after being 330 to 340 pounds last year. He said he does not think that Herrion was using any weight-loss supplements containing ephedra, which is on the NFL's list of banned substances after being linked to many deaths nationwide.

"I really don't think that's the case," the agent said. "He hated to take any kind of drugs, even aspirin. I know he didn't drink. I know he didn't smoke."

NFL Commissioner Paul Tagliabue was in touch with 49ers officials Sunday, and league spokesman Greg Aiello said from New York: "Our thoughts are with the Herrion family and the 49ers. We will be in contact with the 49ers to learn what happened."

Nolan said he learned of Herrion's death before leaving the stadium Saturday night and informed his players in a hangar at the airport after the team passed through security. The 49ers flew back to San Francisco and got back to their training facility around 4 a.m. There was no practice Sunday. The 49ers are scheduled to practice Monday afternoon, and Nolan said a memorial service involving the team will take place Tuesday.

"When something like that happens, you need time to get your head together," 49ers rookie cornerback Daven Holly said. "Our prayers go out to his family. It was a tragedy, and we pray for him and his family. It hits home. It could have been any one of us. It lets you know this is life, too."

Nolan recalled that recently the team prompted rookie quarterback Alex Smith, the top overall selection in this year's NFL draft out of Utah, to stand and sing the Utes' fight song. Herrion promptly stood and joined his former college teammate.

"Everybody got to whooping and hollering," Nolan said. "At that time, a guy comes out of his shell. It was kind of warming to see him."

Said Lyles: "He was a really good guy, a fun-loving guy. He was a kid who really had to work for everything he got. When he told you something, you could count on him. . . . Injuries are part of the game. But the last thing you ever think about is not coming home from a game. It's just tragic."