The Associated Press

LUTZ, Fla. — The Indianapolis Colts’ near-perfect season was plunged into sadness when the news came that coach Tony Dungy’s eldest son was found dead of an apparent suicide.

‘‘Everybody said a team prayer for Coach Dungy and his family,’’ quarterback Peyton Manning said. ‘‘It’s laying on the hearts of all the players here today.’’

James Dungy, the 18-year-old who became a fixture around the teams his father coached and was often mistaken for a player because of his towering size, was found dead in a Tampa-area apartment early Thursday.

His girlfriend returned to the Campus Lodge Apartments at about 1:30 a.m. and found him unresponsive, Hillsborough County Sheriff’s spokeswoman Debbie Carter said. Carter said evidence at the scene indicated he had killed himself.

A sheriff’s deputy performed CPR before an ambulance took him to University Community Hospital, where he was pronounced dead.

Tony Dungy took the team plane from Indianapolis to Tampa, Fla., where he had coached the Buccaneers from 1996 to 2001. He left his team with instructions befitting their ever-steady leader: Keep playing.

‘‘He’s an amazing individual with great strength and integrity, even in the toughest times,’’ assistant head coach Jim Caldwell, who will take over in Dungy’s absence, said after Thursday’s practice. ‘‘He told us to carry on as usual.’’

The Colts (13-1) travel to Seattle for a game Saturday, and team president Bill Polian said Caldwell will lead the team ‘‘for however long Tony will be away, and however long he will be away is entirely up to him.’’

The Seahawks took a knee on the practice field in Kirkland, Wash., on Thursday and bowed their heads for a moment of silence. Seattle coach Mike Holmgren acknowledged that it will be somewhat awkward to coach against the Colts with all they are suddenly enduring.

‘‘Yeah, it is, but we must separate that,’’ he said. ‘‘We still have a lot at stake. We must be able to do that. So that is what we are going to do.’’

Dungy is immensely popular around the league and known for his soft-spoken style and commitment to balancing family life with football — a rare trait in NFL coaches. He shared the blame when Indianapolis lost its first game Sunday against the visiting San Diego Chargers, ending what had been a perfect season.

‘‘It certainly keeps things in perspective,’’ Manning said. ‘‘Players with families, it certainly hits home. Coach Dungy’s close to a lot of these players. … Players feel close to him as well as his family.’’

The Dungys have four other children: daughters Tiara and Jade and sons Eric and Jordan. James Dungy spent his senior year at North Central High School in Indianapolis and graduated this year.

C.E. Quandt, the school’s principal, said Dungy was a personable student who never flaunted his father’s position, and had recently visited North Central. He said the death surprised and saddened everyone at the school.

‘‘It kind of diminishes our school family,’’ he said.

A woman who answered the door at James Dungy’s girlfriend’s home declined comment Thursday. Jessica James, 18, who described herself as a close friend, said she and a group of friends went to the movies with Dungy on Monday night.

‘‘He was cracking jokes, just being himself,’’ she said. ‘‘This morning, it was so surreal.’’

She said Dungy ‘‘was just a really good kid, very laid-back. Unless you asked him, you’d never know he was Tony Dungy’s son.’’

The mood was somber Thursday at the Buccaneers’ practice facility, located near the airport where the Colts’ plane that brought Tony Dungy to Florida was parked. Players and coaches could see the plane from the practice field.

‘‘It shakes you, there’s no doubt about it. Tony and I first came together in 1992 and I got to see the boy grow up. … Tony’s got tremendous faith, and that’s what will carry Tony through,’’ said Bucs defensive coordinator Monte Kiffin, who worked for Dungy at Tampa Bay.

James Dungy was a frequent visitor to the Bucs’ practices and games when his father coached the team.

‘‘He was here all the time, hanging out in the locker room and with the players on the field,’’ fullback Mike Alstott said. ‘‘If James wasn’t here, it was like: ‘Where’s James?’ He was part of this football team.’’

New York Jets coach Herman Edwards, one of Dungy’s closest friends, called James a ‘‘very, very good kid.

‘‘The whole family is good people. You know Tony, how he raised a family,’’ Edwards said from Jets training camp in Hempstead, N.Y. ‘‘A tragedy.’’

Two other NFL head coaches lost close family members this season, both in November. Don Parcells, brother of Dallas Cowboys coach Bill Parcells, died of brain cancer in New Jersey at age 62; Steve Belichick, father of New England Patriots’ coach Bill Belichick, died at 86.

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Associated Press Writers Cliff Brunt in Indianapolis and Mitch Stacy in Tampa, Fla.,; and AP Sports Writers Andrea Adelson in New York and Mike Marot in Indianapolis contributed to this report.