Former NFL star linebacker Junior Seau was found dead Wednesday at his home in Oceanside, California.

Police said Seau died of a gunshot wound to the chest. They are investigating it as a suicide.

Seau was 43 years old.

According to Oceanside police chief Frank McCoy, a call was placed by Seau's girlfriend at 9:35 a.m. local time Wednesday morning. She had returned home and found Seau unconscious with a gunshot wound to the chest.

Police and fire department personnel arrived and found Seau in one of the bedrooms. McCoy said life-saving efforts were performed and were not successful.

"Our hearts and prayers of the city go out to Seau's family," said the chief, who added he would not be able to answer any questions.

Seau spent 13 seasons with the Chargers, helping the franchise to its only Super Bowl appearance after the 1994 season. He also played three seasons for Miami and four more for New England before retiring after the 2009 campaign.

"Everyone at the Chargers is in complete shock and disbelief right now," the Chargers said in a statement. "We ask everyone to stop what they're doing and send their prayers to Junior and his family."

Seau was a 12-time Pro Bowl selection during his 20-year pro career. He was inducted into the Chargers Hall of Fame this past November.

He is the eighth member of San Diego's Super Bowl team to pass away, joining linebackers Lew Bush, Dave Griggs and Doug Miller, running back Rodney Culver, defensive linemen Shawn Lee and Chris Mims and center Curtis Whitley.

"All of us are deeply saddened about Junior Seau, a great player loved by teammates who also worked hard to serve his community," said NFL commissioner Roger Goodell in a statement. "Junior and his family will remain in our thoughts."

Reactions poured in from across the sport, some in the form of statements and some on social media. Ex-teammates, like fellow former linebacker Jason Taylor talked of Seau's personality on an off the field.

Saints quarterback Drew Brees, who played with Seau for two seasons in San Diego, said he was sad to hear the news.

"Junebug. Buddy," Brees wrote on Twitter. "The greatest teammate a young guy could ask for. This is a sad day. He will be missed greatly."

Broncos quarterback Peyton Manning said Seau and Bruce Smith were the two most dominating defenders when he entered the league in 1998. Manning called Seau and Ray Lewis the best linebackers he ever played against.

"Junior was truly a once-in-a-lifetime player," Manning said. "I remember how many times we would be getting ready to play him and the Chargers and someone would say, 'This is a blitz here.' And I would say, 'That's not a blitz; that's just Junior Seau smelling something and going after it.'

"He was very difficult to play against because his instincts would always lead him to the right place on defense -- or the wrong place for the offense."

San Diego Padres president Tom Garfinkel offered condolences on behalf of the team and called Seau "a great San Diegan and an inspiration, not only on the playing field, but in how he positively impacted people's lives."

In October 2010, Seau was hospitalized after driving his car off a cliff in Carlsbad, California just hours after being arrested on suspicion of domestic violence in the wake of an incident with his live-in girlfriend. He was never charged.

Speculation had surfaced at the time that Seau was trying to kill himself, but he said he fell asleep at the wheel.