Colts general manager Chris Ballard told reporters on a conference call Tuesday night that Luck's calf strain has developed into a high-ankle issue. Ballard said Luck "most likely" won't play in the preseason because of the injury.
"In the course of dealing with this calf injury, it appears that now we've got an ankle issue," Ballard said. "There's no question that he had a calf [strain], but the lower part is more of an ankle issue. Once we get that under control, we think we can help with the pain.
"Once we get that under control then we can really move forward. All players need reps and he knows that, and he knows he needs to get out there and get his reps. So we'll play that kind of day-to-day."
Luck was ruled out of practices through Thursday, including joint sessions with the Cleveland Browns this week, according to the team. The quarterback has participated in walk-throughs and has worked with throwing coach Tom House.
Ballard didn't provide a timetable for Luck's return, but hopes to have the eighth-year quarterback under center in Week 1 against the Los Angeles Chargers.
"We're three and a half weeks away from the regular season, so I'm not ready to say [Luck's season is in jeopardy]," Ballard said.
In 16 regular-season games last season, Luck completed a career-high 67.3 percent of his passes with 4,593 yards, 39 touchdowns and 15 interceptions.