Luck, who turns 30 on Sept. 12, already has met with Colts owner Jim Irsay to tell him of the decision, the source said.
There will be a news conference Sunday to make it official, but Luck is mentally worn down, and now checking out, the source said.
Luck has been dealing with injury throughout training camp, and has yet to play in a preseason game. A calf strain originally diagnosed in March first hobbled him, but tests earlier this month showed him having pain in the “high anklish” area of his left leg.
The Colts played their third preseason game Saturday night in Indianapolis against the Bears. Luck already had been ruled out of the game, but was seen on the sideline, laughing and conversing with teammates.
His retirement means Jacoby Brissett is in line to start for the Colts in Week 1 against the Chargers. They play Sept. 8, in Los Angeles.
Injuries have derailed what was a promising start to Luck’s NFL career. He led the Colts to the playoffs in each of first three seasons, including the AFC Championship Game in 2014, before a shoulder injury in Week 3 of the 2015 was the start of numerous injuries for Luck. He has missed 26 games, including the entire 2017 season due to shoulder, kidney and rib problems since the 2015 season.
The Colts went 4-12 in 2017 when Luck was out. He passed for 4,593 yards, 39 touchdowns and was named the NFL’s Most Improved Player last season.
It’s stunning news for a Colts team that went to the second round of the playoffs last season and in the eyes of many had a Super Bowl-caliber roster in 2019. Now, the Colts will turn to Brissett, the 26-year-old quarterback acquired from the Patriots in 2017.
With Luck dealing with a variety of injuries in 2017, Brissett started 15 games for Indy, throwing for 3,098 yards, with 13 touchdowns and seven interceptions.