Luck told the NFL Network that he sprained the AC joint in his throwing shoulder in a snowboarding accident in Colorado. The injury, the 28-year-old said, came after -- and was separate from -- the torn labrum he sustained early in the 2015 season.
The labrum tear resulted in surgery and cost Luck all of the 2017 season.
Luck said he immediately told the Colts about the snowboarding injury.
"This was after the initial injury," Luck said, via the NFL Network. "I went back, rehabbed it with the Colts. I've had a bunch of AC sprains, both left and right shoulder, and resolved that issue. But the labrum has been my issue, was my issue, what I worked through, what I got surgery on."
Luck said the AC injury had no effect on his labrum tear.
"I've seen more doctors than I can count on two hands over the past two or three years," Luck said, "and the consensus -- unanimous -- is that the AC is not an issue, nor did it have an effect. The labrum is an issue."
Snowboarding is also not the issue anymore, Luck said.
"I'm obviously not snowboarding anymore," said Luck, who played in his first game since returning from injury against the Cincinnati Bengals on Sunday at Lucas Oil Stadium.
Luck completed 20 of 32 passes for 204 yards with one touchdown and one interception in three preseason games.
After starting all 16 games in each of his first three seasons and guiding Indianapolis to identical 11-5 records, Luck was limited to seven starts in 2015. He made 15 starts in 2016, throwing for 4,240 yards and 31 touchdowns versus 13 interceptions.
The Colts finished 4-12 in 2017 with Jacoby Brissett starting 15 games at quarterback. Recurring soreness in Luck's shoulder prompted the Colts to finally shut him down two weeks after he returned to practice in early October. He was placed on injured reserve on Nov. 2.